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Pearson Physics

James S. Walker

Chapter 6

Work and Energy - all with Video Answers

Educators


Chapter Questions

01:04

Problem 1

If the force exerted by the intern is doubled and the distance is halved, does the work done by the intern increase, decrease, or remain the same?

Vysakh M
Vysakh M
Numerade Educator
01:03

Problem 2

There is a species of Darwin's finch on the Galapagos Islands that can exert a force of $205 \mathrm{~N}$ with its beak as it cracks open a seed case. If its beak moves through a distance of $0.40 \mathrm{~cm}$ during this operation, how much work does the finch do to get at the seed inside the case?

Prabhu Ramji
Prabhu Ramji
Numerade Educator
00:46

Problem 3

Early one October you go to a pumpkin patch to select your Halloween pumpkin. You lift a $3.2-\mathrm{kg}$ pumpkin to a height of $0.80 \mathrm{~m}$ to check it out. How much work do you do on the pumpkin when you lift it from the ground?

Vysakh M
Vysakh M
Numerade Educator
01:14

Problem 4

Follow-up Suppose the lifeboat slides halfway to the water, gets stuck for a moment, and then starts up again and continues to the end of the ramp. What is the work done by gravity in this case?

Prabhu Ramji
Prabhu Ramji
Numerade Educator
01:11

Problem 5

A parent pulls a child in a little red wagon with constant speed. If the parent pulls with a force of $16 \mathrm{~N}$ for $12 \mathrm{~m}$ and the handle of the wagon is inclined at an angle of $25^{\circ}$ above the horizontal, how much work does the parent do on the wagon?

Prabhu Ramji
Prabhu Ramji
Numerade Educator
03:18

Problem 6

The frictional force acting on the drum set does negative work. Does friction always do negative work? If yes, explain why. If no, give an example of friction doing positive work.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
03:21

Problem 7

You slide a 0.12-kg coffee mug $0.15 \mathrm{~m}$ across a table. The force you exert is horizontal and of magnitude $0.10 \mathrm{~N}$. The coefficient of kinetic friction between the mug and the table is $0.05$. How much work is done on the mug?

Prabhu Ramji
Prabhu Ramji
Numerade Educator
02:10

Problem 8

How is work calculated when force and displacement are in the same direction?

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
04:23

Problem 9

Which component of force is used to calculate work when the force and the displacement are at an angle to each other?

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
01:41

Problem 10

Assess Is it possible to do work on an object that remains at rest? Explain.

Prabhu Ramji
Prabhu Ramji
Numerade Educator
02:39

Problem 11

Give two examples of (a) positive work done by a frictional force (if possible) and (b) negative work done by a frictional force.

Prabhu Ramji
Prabhu Ramji
Numerade Educator
01:15

Problem 12

A child in a tree house uses a rope attached to a basket to lift a $22-\mathrm{N}$ dog upward through a distance of $4.7 \mathrm{~m}$ into the house. How much work does the child do in lifting the dog?

Narayan Hari
Narayan Hari
Numerade Educator
01:32

Problem 13

To move a suitcase up to the check-in stand at an airport, a student pushes with a horizontal force through a distance of $0.95 \mathrm{~m}$. If the work done by the student is $32 \mathrm{~J}$, what is the magnitude of the force he exerts?

Narayan Hari
Narayan Hari
Numerade Educator
01:26

Problem 14

A farmhand pushes a bale of hay $3.9 \mathrm{~m}$ across the floor of a barn. She exerts a force of $88 \mathrm{~N}$ at an angle of $25^{\circ}$ below the horizontal. How much work has she done?

Narayan Hari
Narayan Hari
Numerade Educator
03:42

Problem 15

The coefficient of kinetic friction between a large box and the floor is $0.21$. A person pushes horizontally on the box with a force of $160 \mathrm{~N}$ for a distance of $2.3 \mathrm{~m}$. If the mass of the box is $72 \mathrm{~kg}$, what is the total work done on the box?

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
01:10

Problem 16

A $13-\mathrm{g}$ goldfinch has a speed of $8.5 \mathrm{~m} / \mathrm{s}$. What is its kinetic energy?

Prabhu Ramji
Prabhu Ramji
Numerade Educator
01:34

Problem 17

The kinetic energy of a small boat is $15,000 \mathrm{~J}$. If the boat's speed is $5.0 \mathrm{~m} / \mathrm{s}$, what is its mass?

Narayan Hari
Narayan Hari
Numerade Educator
01:19

Problem 18

What is the speed of a $0.15-\mathrm{kg}$ baseball whose kinetic energy is $77 \mathrm{~J}$ ?

Narayan Hari
Narayan Hari
Numerade Educator
01:55

Problem 19

Do you expect the change in kinetic energy of the box to be greater than, less than, or equal to $19.9 \mathrm{~J}$ ? Verify your answer by calculating the change in its kinetic energy.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
02:08

Problem 20

At $t=1.0 \mathrm{~s}$, a $0.40-\mathrm{kg}$ object is falling with a speed of $6.0 \mathrm{~m} / \mathrm{s}$. At $t=2.0 \mathrm{~s}$, it has a kinetic energy of $25 \mathrm{~J}$.
(a) What is the kinetic energy of the object at $t=1.0 \mathrm{~s}$ ?
(b) What is the speed of the object at $t=2.0 \mathrm{~s}$ ?
(c) How much work was done on the object between $t=1.0 \mathrm{~s}$ and $t=2.0 \mathrm{~s}$ ?

Prabhu Ramji
Prabhu Ramji
Numerade Educator
01:15

Problem 21

As an Acapulco cliff diver drops to the water from a height of $46 \mathrm{~m}$, his gravitational potential energy decreases by $25,000 \mathrm{~J}$. What is the diver's weight in newtons?

Prabhu Ramji
Prabhu Ramji
Numerade Educator
01:54

Problem 22

If the mass of the mountain climber is increasedby adding more items to his backpack, for example-does the possible altitude gain increase, decrease, or stay the same? Calculate the altitude gain for a climber with a mass of $91.0 \mathrm{~kg}$.

Prabhu Ramji
Prabhu Ramji
Numerade Educator
01:11

Problem 23

What is the gravitational potential energy of a $0.25-\mathrm{kg}$ ball when it is $1.3 \mathrm{~m}$ above the floor?

Prabhu Ramji
Prabhu Ramji
Numerade Educator
01:14

Problem 24

The gravitational potential energy of a person on a $3.0-\mathrm{m}-\mathrm{high}$ diving board is $1800 \mathrm{~J}$. What is the person's mass?

Narayan Hari
Narayan Hari
Numerade Educator
01:25

Problem 25

How far must a spring with a spring constant of $85 \mathrm{~N} / \mathrm{m}$ be stretched to store $0.22 \mathrm{~J}$ of potential energy?

Narayan Hari
Narayan Hari
Numerade Educator
01:28

Problem 26

A hockey stick stores $4.2 \mathrm{~J}$ of potential energy when it is bent $3.1 \mathrm{~cm}$. Treating the hockey stick as a spring, what is its spring constant?

Prabhu Ramji
Prabhu Ramji
Numerade Educator
01:39

Problem 27

How does the kinetic energy of an object change if its speed doubles? Triples?

Vysakh M
Vysakh M
Numerade Educator
01:39

Problem 28

If positive work is done on an object, does its kinetic energy increase, decrease, or stay the same? Explain.

Prabhu Ramji
Prabhu Ramji
Numerade Educator
01:37

Problem 29

A pitcher throws a baseball at $40 \mathrm{~m} / \mathrm{s}(\sim 90 \mathrm{mph})$, and the catcher stops it in her glove. Is the work done on the ball by the catcher positive, negative, or zero? Explain.

Prabhu Ramji
Prabhu Ramji
Numerade Educator
01:13

Problem 30

Is the change in potential energy when a box is lifted 1 meter off the ground the same on Earth and the Moon? Explain.

Jacob Shpiece
Jacob Shpiece
Numerade Educator
01:25

Problem 31

How does the potential energy of a spring change if its amount of stretch is doubled?c

Prabhu Ramji
Prabhu Ramji
Numerade Educator
01:40

Problem 32

A $9.50-\mathrm{g}$ bullet has a speed of $1.30 \mathrm{~km} / \mathrm{s}$. What is the kinetic energy of the bullet?

Prabhat Tyagi
Prabhat Tyagi
Numerade Educator
00:47

Problem 33

A $0.27-\mathrm{kg}$ volleyball has a kinetic energy of $7.8 \mathrm{~J}$. What is the speed of the volleyball?

Jacob Shpiece
Jacob Shpiece
Numerade Educator
01:18

Problem 34

How much work is required for a $73-\mathrm{kg}$ runner to accelerate from rest to a speed of $7.5 \mathrm{~m} / \mathrm{s}$ ?

Narayan Hari
Narayan Hari
Numerade Educator
01:26

Problem 35

A $0.14-\mathrm{kg}$ pinecone is $16 \mathrm{~m}$ above the ground. What is its gravitational potential energy?

Narayan Hari
Narayan Hari
Numerade Educator
01:23

Problem 36

It takes $13 \mathrm{~N}$ to stretch a certain spring $9.5 \mathrm{~cm}$. How much potential energy is stored in this spring? (Hint: Calculate the spring constant first, then the potential energy.)

Prabhu Ramji
Prabhu Ramji
Numerade Educator
02:40

Problem 37

If the mass of the ball were increased, would its speed just before it is caught be greater than, less than, or the same as the value we just found? Assume that everything else remains the same.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
01:36

Problem 38

In a tennis match a player wins a point by hitting the $0.059-\mathrm{kg}$ ball sharply to the ground on the opponent's side of the net. If the ball bounces upward from the ground with a speed of $16 \mathrm{~m} / \mathrm{s}$ and is caught by a fan in the stands when it has a speed of $12 \mathrm{~m} / \mathrm{s}$, how high above the court is the fan? Ignore air resistance.

Prabhu Ramji
Prabhu Ramji
Numerade Educator
02:11

Problem 39

A crow drops a 0.11-kg clam onto a rocky beach from a height of $9.8 \mathrm{~m}$. What is the kinetic energy of the clam when it is $5.0 \mathrm{~m}$ above the ground? What is its speed at that point?

Prabhu Ramji
Prabhu Ramji
Numerade Educator
00:42

Problem 40

The potential energy of an object decreases by $10 \mathrm{~J}$. What is the change in the object's kinetic energy, assuming there is no friction in the system?

Jacob Shpiece
Jacob Shpiece
Numerade Educator
00:43

Problem 41

Big ldea What is the necessary condition for the mechanical energy of a system to be conserved?

Jacob Shpiece
Jacob Shpiece
Numerade Educator
02:35

Problem 42

Analyze Discuss the various energy conversions that occur when a person performs a pole vault. Include as many conversions as you can. Be sure to consider times before, during, and after the vault itself.

Prabhu Ramji
Prabhu Ramji
Numerade Educator
04:10

Problem 43

You throw a ball straight up into the air. It reaches a maximum height and returns to your hand. At what location(s) is the kinetic energy of the ball (a) a maximum and (b) a minimum? At what location(s) is the potential energy of the ball (c) a maximum and (d) a minimum?

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
02:06

Problem 44

At an amusement park, a swimmer uses a water slide to enter the main pool. If the swimmer starts at rest, slides without friction, and descends through a vertical height of $2.31 \mathrm{~m}$, what is her speed at the bottom of the slide?

Yaqub Khan
Yaqub Khan
Numerade Educator
03:49

Problem 45

A $0.21-\mathrm{kg}$ apple falls from a tree to the ground, $4.0 \mathrm{~m}$ below. Ignoring air resistance, determine the apple's kinetic energy, $K E$, the gravitational potential energy of the system, $P E_{\text {gravity, }}$ and the total mechanical energy of the system, $E$, when the apple's height above the ground is $3.0 \mathrm{~m}$.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
01:52

Problem 46

You throw a baseball glove straight upward to celebrate a victory. Its initial kinetic energy is $K E$, and it reaches a maximum height $h$. What is the kinetic energy of the glove when it is at the height $h / 2$ ?

Eric Mockensturm
Eric Mockensturm
Numerade Educator
01:39

Problem 47

Engine 1 does twice the work of engine 2. Is it correct to conclude that engine 1 produces twice as much power as engine 2? Explain.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
01:51

Problem 48

A record for running up the stairs of the Empire State Building was set on February 3, 2003. The runner completed the 86 flights, with a total of 1576 steps, in $9 \mathrm{~min} 33 \mathrm{~s}$. If the altitude gain for each step was $0.20 \mathrm{~m}$ and the mass of the runner was $70.0 \mathrm{~kg}$, what was his average power output during the climb? Give your answer in both watts and horsepower.

Prabhu Ramji
Prabhu Ramji
Numerade Educator
01:46

Problem 49

Find the time required to accelerate from $17.9 \mathrm{~m} / \mathrm{s}$ to $22.4 \mathrm{~m} / \mathrm{s}$ with $3.05 \times 10^{4} \mathrm{~W}$ of power.

Narayan Hari
Narayan Hari
Numerade Educator
02:36

Problem 50

A pitcher accelerates a $0.14-\mathrm{kg}$ hardball from rest to $42.5 \mathrm{~m} / \mathrm{s}$ in $0.060 \mathrm{~s}$.
(a) How much work does the pitcher do on the ball?
(b) What is the pitcher's power output during the pitch?

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
01:05

Problem 51

A small motor runs a lift that raises a load of bricks weighing $836 \mathrm{~N}$ to a height of $10.7 \mathrm{~m}$ in $23.2 \mathrm{~s}$. Assuming that the bricks are lifted with constant speed, what is the minimum power the motor must produce?

Eric Mockensturm
Eric Mockensturm
Numerade Educator
01:19

Problem 52

If the rate at which work is done on an object is increased, does the power supplied to that object increase, decrease, or stay the same?

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
01:37

Problem 53

System 1 has a force of $10 \mathrm{~N}$ and a speed of $5 \mathrm{~m} / \mathrm{s}$. System 2 has a force of $20 \mathrm{~N}$ and a speed of $2 \mathrm{~m} / \mathrm{s}$. Which system has the greater power? Explain.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
01:39

Problem 54

Engine 1 produces twice the power of engine 2 . Is it correct to conclude that engine 1 does twice as much work as engine 2? Explain.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
01:48

Problem 55

Football player 1 exerts twice the force of football player 2. Is it correct to conclude that football player 1 produces twice as much power as football player 2? Explain.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
02:08

Problem 56

You raise a bucket of water from the bottom of a well that is $12 \mathrm{~m}$ deep. The mass of the bucket and the water is $5.00 \mathrm{~kg}$, and it takes $15 \mathrm{~s}$ to raise the bucket to the top of the well. How much power is required?

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
01:51

Problem 57

What is the power output of a 1.4-g fly as it walks straight up a windowpane at $2.3 \mathrm{~cm} / \mathrm{s}$ ?

Narayan Hari
Narayan Hari
Numerade Educator
01:28

Problem 58

A kayaker paddles with a power output of $50.0 \mathrm{~W}$ to maintain a steady speed of $1.50 \mathrm{~m} / \mathrm{s}$. Find the force exerted by the kayaker.

Narayan Hari
Narayan Hari
Numerade Educator
01:09

Problem 59

An ice cube is placed in a microwave oven. Suppose the oven delivers $105 \mathrm{~W}$ of power to the ice cube and it takes $32,200 \mathrm{~J}$ to melt it. How long does it take for the ice cube to melt?

Jacob Shpiece
Jacob Shpiece
Numerade Educator
01:36

Problem 60

A friend makes this statement: "Only the component of force perpendicular to the direction of motion does work." Is this statement true or false? Explain.

Nishant Kumar
Nishant Kumar
Numerade Educator
01:10

Problem 61

In the equation $W=F d \cos \theta$, what is the angle $\theta$ ?

Jacob Shpiece
Jacob Shpiece
Numerade Educator
01:11

Problem 62

The general equation for work is $W=F d \cos \theta$. For what angle is the work $W=F d$ ? For what angle is the work $W=-F d$ ?

Jacob Shpiece
Jacob Shpiece
Numerade Educator
02:02

Problem 63

Your favorite uncle makes this statement: "A force that is always perpendicular to the velocity of a particle does no work on the particle." Is this statement true or false?
If it is true, state why. If it is false, give a counterexample.

Nishant Kumar
Nishant Kumar
Numerade Educator
01:39

Problem 64

Triple Choice The International Space Station orbits the Earth in an approximately circular orbit at a height of $h=375 \mathrm{~km}$ above the Earth's surface. In one complete orbit, is the work done by Earth's gravity on the space station positive, negative, or zero? Explain.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
04:10

Problem 65

Triple Choice A pendulum bob swings from point $A$ to point B along the circular arc indicated in Figure 6.10.
(a) Is the work done on the bob by gravity positive, negative, or zero? Explain. (b) Is the work done on the bob by the string positive, negative, or zero? Explain.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
04:11

Problem 66

A pendulum bob swings from point B to point $C$ along the circular arc indicated in Figure 6.10. (a) Is the work done on the bob by gravity positive, negative, or zero? Explain. (b) Is the work done on the bob by the string positive, negative, or zero? Explain.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
00:50

Problem 67

A dog lifts a $0.75-\mathrm{kg}$ bone straight up through a distance of $0.11 \mathrm{~m}$. How much work was done by the dog?

Vysakh M
Vysakh M
Numerade Educator
01:00

Problem 68

A weightlifter does $9.8 \mathrm{~J}$ of work while lifting a weight straight upward through a distance of $0.12 \mathrm{~m}$. What was the force exerted by the weightlifter?

Jacob Shpiece
Jacob Shpiece
Numerade Educator
01:09

Problem 69

You do $13 \mathrm{~J}$ of work as you lift a $35-\mathrm{N}$ pail of water. Through what height did you lift the pail?

Vysakh M
Vysakh M
Numerade Educator
01:30

Problem 70

You push a book $0.45 \mathrm{~m}$ across a desk with a $5.2-\mathrm{N}$ force that is at an angle of $21^{\circ}$ below the horizontal. How much work did you do on the book?

Nishant Kumar
Nishant Kumar
Numerade Educator
03:55

Problem 71

You pick up a $3.4-\mathrm{kg}$ can of paint from the ground and lift it to a height of $1.8 \mathrm{~m}$. (a) How much work do you do on the can of paint? (b) You hold the can stationary for half a minute, waiting for a friend on a ladder to take it. How much work do you do during this time? (c) Your friend decides not to use the paint, so you lower it back to the ground. How much work do you do on the can as you lower it?

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
02:30

Problem 72

A tow rope, parallel to the water, pulls a water skier directly behind a boat with constant velocity for a distance of $65 \mathrm{~m}$ before the skier falls. The tension in the rope is $120 \mathrm{~N}$. (a) Is the work done on the skier by the rope positive, negative, or zero? Explain. (b) Calculate the work done by the rope on the skier.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
01:52

Problem 73

In Problem 72, (a) is the work done on the boat by the rope positive, negative, or zero? done on the boat by the rope positive, negative, or zero? Explain. (b) Calculate the work done by the rope on the boat.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
01:18

Problem 74

A child pulls a friend in a little red wagon. If the child pulls with a force of $16 \mathrm{~N}$ for $12 \mathrm{~m}$ and the handle of the wagon is inclined at an angle of $25^{\circ}$ above the horizontal, how much work does the child do on the wagon?

Nishant Kumar
Nishant Kumar
Numerade Educator
01:50

Problem 75

A 51-kg packing crate is pulled across a rough floor with a rope that is at an angle of $43^{\circ}$ above the horizontal. If the tension in the rope is $120 \mathrm{~N}$, how much work is done on the crate to move it $18 \mathrm{~m}$ ?

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
02:44

Problem 76

Water skiers often ride to one side of the center line of a boat, as shown in Figure 6.11. In this case the boat is traveling at $15 \mathrm{~m} / \mathrm{s}$, and the tension in the rope is $75 \mathrm{~N}$. If the boat does $2500 \mathrm{~J}$ of work on the skier in $42 \mathrm{~m}$, what is the angle $\theta$ between the tow rope and the center line of the boat?

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
01:57

Problem 77

A package rests on the floor of an elevator that is rising with constant speed. The elevator exerts an upward force on the package and thus does positive work on it. Why doesn't the kinetic energy of the package increase?

James Kiss
James Kiss
Numerade Educator
02:28

Problem 78

An object moves with constant velocity. Is it safe to conclude that no force acts on the object? Why, or why not?

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
02:42

Problem 79

Rank Four joggers have the following masses and
$$
\begin{array}{|c|c|c|}
\hline \text { Jogger } & \text { Mass } & \text { Speed } \\
\hline \text { A } & m & v \\
\hline \text { B } & m / 2 & 3 v \\
\hline C & 3 m & v / 2 \\
\hline D & 4 m & v / 2 \\
\hline
\end{array}
$$
Rank the joggers in order of increasing kinetic energy. Indicate ties where appropriate.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
01:13

Problem 80

Is it possible for the kinetic energy of an object to be negative? Explain.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
05:09

Problem 81

The work required to accelerate a car from 0 to $50 \mathrm{~km} / \mathrm{h}$ is $W$. (a) Is the work required to accelerate the car from $50 \mathrm{~km} / \mathrm{h}$ to $150 \mathrm{~km} / \mathrm{h}$ equal to $2 W, 3 W, 8 W$, or $9 W$ ? (b) Choose the best explanation from among the following:

A. The work to accelerate the car depends on the speed squared.
B. The final speed is three times the speed that was produced by the work $W$.
C. The increase in speed from $50 \mathrm{~km} / \mathrm{h}$ to $150 \mathrm{~km} / \mathrm{h}$ is twice the increase in speed from 0 to $50 \mathrm{~km} / \mathrm{h}$.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
02:47

Problem 82

Ball 1 is dropped to the ground from rest. Ball 2 is thrown to the ground with an initial downward speed. Assuming that the balls have the same mass and are released from the same height, is the change in gravitational potential energy of ball 1 greater than, less than, or equal to the change in gravitational potential energy of ball 2? (b) Choose the best explanation from among the following:

A. Ball 2 has the greater total energy, and therefore more of its energy can go into gravitational potential energy.
B. The gravitational potential energy depends only on the mass of the ball and its initial height above the ground.
C. All of the initial energy of ball 1 is gravitational potential energy.

Khoobchandra Agrawal
Khoobchandra Agrawal
Numerade Educator
02:13

Problem 83

Referring to Figure 6.10, is the gravitational potential energy of the bob at point $C$ greater than, less than, or equal to the gravitational potential energy at (a) point $A$ and (b) point B? Explain.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
02:09

Problem 84

The potential energy of a stretched spring is positive. Is the potential energy of a compressed spring positive, negative, or zero? Explain.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
01:11

Problem 85

When NASA's Skylab reentered the Earth's atmosphere on July 11,1979 , it broke into a myriad of pieces. One of the largest fragments was a $1770-\mathrm{kg}$ lead-lined film vault, and it landed with an estimated speed of $120 \mathrm{~m} / \mathrm{s}$. What was the kinetic energy of the film vault when it landed?

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
01:22

Problem 86

A $7.3-\mathrm{kg}$ bowling ball is placed on a shelf $1.7 \mathrm{~m}$ above the floor. What is its gravitational potential energy?

Narayan Hari
Narayan Hari
Numerade Educator
01:18

Problem 87

A $0.15-\mathrm{kg}$ baseball has a kinetic energy of $18 \mathrm{~J}$. What is its speed?

Narayan Hari
Narayan Hari
Numerade Educator
01:23

Problem 88

The gravitational potential energy of a $0.12-\mathrm{kg}$ bird in a tree is $6.6 \mathrm{~J}$. What is the height of the bird above the ground?

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
01:23

Problem 89

A spring with a spring constant of $92 \mathrm{~N} / \mathrm{m}$ is compressed by $2.8 \mathrm{~cm}$. How much potential energy is stored in the spring?

Narayan Hari
Narayan Hari
Numerade Educator
01:28

Problem 90

A force of $27 \mathrm{~N}$ stretches a given spring by $4.4 \mathrm{~cm}$. How much potential energy is stored in the spring when it is compressed $3.5 \mathrm{~cm}$ ?

Narayan Hari
Narayan Hari
Numerade Educator
01:50

Problem 91

A spring that is stretched $2.6 \mathrm{~cm}$ stores a potential energy of $0.053 \mathrm{~J}$. What is the spring constant of this spring?

Prabhat Tyagi
Prabhat Tyagi
Numerade Educator
02:53

Problem 92

A 1100-kg car is coasting on a horizontal road with a speed of $19 \mathrm{~m} / \mathrm{s}$. After passing over an unpaved, sandy stretch $32 \mathrm{~m}$ long, the car's speed has decreased to $12 \mathrm{~m} / \mathrm{s}$. (a) Was the net work done on the car positive, negative, or zero? Explain.
(b) Find the magnitude of the average net force on the car in the sandy section of the road.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
02:30

Problem 93

A $65-\mathrm{kg}$ bicyclist rides his $8.8-\mathrm{kg}$ bicycle with a speed of $14 \mathrm{~m} / \mathrm{s}$. (a) How much work must be done by the brakes to bring the bike and rider to a stop? (b) What is the magnitude of the braking force if the bicycle comes to rest in $3.5 \mathrm{~m}$ ?

Hubert Agamasu
Hubert Agamasu
Numerade Educator
03:21

Problem 94

After hitting a long fly ball that goes over the right fielder's head and lands in the outfield, a batter decides to keep going past second base and try for third base. The $62-\mathrm{kg}$ player begins sliding $3.4 \mathrm{~m}$ from the base with a speed of $4.5 \mathrm{~m} / \mathrm{s}$. (a) If the player comes to rest at third base, how much work was done on the player by friction with the ground? (b) What was the coefficient of kinetic friction between the player and the ground?

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
02:03

Problem 95

An object has a speed of $3.5 \mathrm{~m} / \mathrm{s}$ and a kinetic energy of $14 \mathrm{~J}$ at $t=0$. At $t=5.0 \mathrm{~s}$ the object has a speed of $4.7 \mathrm{~m} / \mathrm{s}$. (a) What is the mass of the object? (b) What is the kinetic energy of the object at $t=5.0 \mathrm{~s}$ ? (c) How much work was done on the object between $t=0$ and $t=5.0 \mathrm{~s}$ ?

James Kiss
James Kiss
Numerade Educator
00:44

Problem 96

A $0.33-\mathrm{kg}$ pendulum bob is attached to a string $1.2 \mathrm{~m}$ long. What is the change in the gravitational potential energy of the system as the bob swings from point $A$ to point B in Figure 6.12?

Khoobchandra Agrawal
Khoobchandra Agrawal
Numerade Educator
01:24

Problem 97

An object moves with no friction or air resistance. Initially, its kinetic energy is $10 \mathrm{~J}$, and its gravitational potential energy is $20 \mathrm{~J}$. What is its kinetic energy when its potential energy has decreased to $15 \mathrm{~J}$ ? What is its potential energy when its kinetic energy has decreased to $5 \mathrm{~J}$ ?

Melissa Walsh
Melissa Walsh
Numerade Educator
02:58

Problem 98

An object moves with no friction or air resistance. Initially, its kinetic energy is $10 \mathrm{~J}$, and its gravitational potential energy is $30 \mathrm{~J}$. What is the greatest potential energy possible for this object? What is the greatest kinetic energy possible for this object?

Nishant Kumar
Nishant Kumar
Numerade Educator
01:00

Problem 99

You throw a ball upward and let it fall to the ground. Your friend drops an identical ball straight down to the ground from the same height. (a) Is the change in kinetic energy (from just after the ball is released until just before it hits the ground) of your ball greater than, less than, or equal to the change in kinetic energy of your friend's ball? (b) Choose the best explanation from among the following:

A. Your friend's ball converts all of its initial energy into kinetic energy.

B. Your ball is in the air longer, which results in a greater change in kinetic energy.
C. The change in gravitational potential energy is the same for each ball, which means that the change in kinetic energy must also be the same.

James Kiss
James Kiss
Numerade Educator
02:54

Problem 100

Three balls are thrown upward with the same initial speed, $v_{\mathrm{i}}$, but at different angles relative to the horizontal, as shown in Figure 6.13. Ignoring air resistance, indicate which of the following statements $(A, B, C$, or $D)$ is correct when the balls are at the dashed level?
A. Ball 3 has the lowest speed.
B. Ball 1 has the lowest speed.
C. All three balls have the same speed.
D. The speed of the balls depends on their mass.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
02:18

Problem 101

A player passes a $0.600-\mathrm{kg}$ basketball down court for a fast break. The ball leaves the player's hands with a speed of $8.30 \mathrm{~m} / \mathrm{s}$ and slows down to $7.10 \mathrm{~m} / \mathrm{s}$ at its highest point. Ignoring air resistance, how high above the release point is the ball when it is at its maximum height?

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
07:03

Problem 102

A $5.76-\mathrm{kg}$ rock is dropped and allowed to fall freely. Find the initial kinetic energy, the final kinetic energy, and the change in kinetic energy for (a) the first $2.00 \mathrm{~m}$ of fall and (b) the second $2.00 \mathrm{~m}$ of fall.

Yaqub Khan
Yaqub Khan
Numerade Educator
06:21

Problem 103

A $0.26-\mathrm{kg}$ rock is thrown vertically upward from the top of a cliff that is $32 \mathrm{~m}$ high. When it hits the ground at the base of the cliff, the rock has a speed of $29 \mathrm{~m} / \mathrm{s}$. Assuming that air resistance can be ignored, find (a) the initial speed of the rock and (b) the greatest height of the rock as measured from the base of the cliff.

Yaqub Khan
Yaqub Khan
Numerade Educator
01:50

Problem 104

A block with a mass of $3.7 \mathrm{~kg}$ slides with a speed of $2.2 \mathrm{~m} / \mathrm{s}$ on a frictionless surface. The block runs into a stationary spring and compresses it a certain distance before coming to rest. What is the compression distance, given that the spring has a spring constant of $3200 \mathrm{~N} / \mathrm{m}$ ?

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
02:21

Problem 105

A $1.3-\mathrm{kg}$ block is pushed up against a stationary spring, compressing it a distance of $4.2 \mathrm{~cm}$. When the block is released, the spring pushes it away across a frictionless, horizontal surface. What is the speed of the block, given that the spring constant of the spring is $1400 \mathrm{~N} / \mathrm{m}$ ?

Nishant Kumar
Nishant Kumar
Numerade Educator
03:28

Problem 106

Suppose the pendulum bob in Figure $6.12$ has a mass of $0.33 \mathrm{~kg}$ and is moving to the right at point $B$ with a speed of $2.4 \mathrm{~m} / \mathrm{s}$. Air resistance is negligible. (a) What is the change in the system's gravitational potential energy when the bob reaches point $A$ ? (b) What is the speed of the bob at point $A$ ?

James Kiss
James Kiss
Numerade Educator
05:29

Problem 107

(a) In Problem 106, what is the bob's kinetic energy at point B? (b) At some point the bob will come to rest momentarily. Without doing an additional calculation, determine the change in the system's gravitational potential energy between point $B$ and the point where the bob comes to rest. (c) Find the maximum angle the string makes with the vertical as the bob swings back and forth. Ignore air resistance.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
04:20

Problem 108

The two masses in the device shown in Figure 6.14 are initially at rest at the same height. After they are released, the large mass, $m_{2}$, falls through a height $h$ and hits the floor, and the small mass, $m_{1}$, rises through a height $h$. (a) Find the speed of the masses just before $m_{2}$ lands, giving your answer in terms of $m_{1}, m_{2}, g$, and $h$. Assume that the ropes and pulley have negligible mass and that friction can be ignored. (b) Evaluate your answer to part (a) for the case where $h=1.2 \mathrm{~m}$, $m_{1}=3.7 \mathrm{~kg}$, and $m_{2}=4.1 \mathrm{~kg}$.

Supratim Pal
Supratim Pal
Numerade Educator
02:47

Problem 109

Engine 1 produces twice the power of engine 2 . If it takes engine 1 the time $T$ to do the work $W$, how long does it take engine 2 to do the same work? Explain.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
02:45

Problem 110

Engine 1 produces twice the power of engine 2 . If it takes engine 1 the time $T$ to do the work $W$, how long does it take engine 2 to do the work 3 W? Explain.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
01:34

Problem 111

Rank Four forces do the following amounts of work in the indicated times:
$$
\begin{array}{|c|c|c|}
\hline \text { Force } & \text { Work } & \text { Time } \\
\hline \text { A } & 5 J & 105 \\
\hline \text { B } & 3 J & 5 s \\
\hline C & 6 J & 185 \\
\hline D & 25 J & 125 s \\
\hline
\end{array}
$$
Rank these forces in order of increasing power produced. Indicate ties where appropriate.

Melissa Walsh
Melissa Walsh
Numerade Educator
02:01

Problem 112

Four forces do the following amounts of work and produce the indicated powers:
$$
\begin{array}{|c|c|c|}
\hline \text { Force } & \text { Work } & \text { Power } \\
\hline \text { A } & 40\rfloor & 80 W \\
\hline \text { B } & 35\rfloor & 5 W \\
\hline \text { C } & 75\rfloor & 25 \mathrm{~W} \\
\hline \text { D } & 60\rfloor & 30 \mathrm{~W} \\
\hline
\end{array}
$$
Rank these forces in order of increasing time required to do the work. Indicate ties where appropriate.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
01:39

Problem 113

How many joules of energy are in a kilowatt-hour?

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
01:41

Problem 114

Estimate the power you produce as you walk leisurely up a flight of stairs.
Give your answer in both watts and horsepower $(1 \mathrm{hp}=746 \mathrm{~W})$.

Melissa Walsh
Melissa Walsh
Numerade Educator
01:37

Problem 115

As you lift an 88-N box straight upward, you produce a power of $72 \mathrm{~W}$. What is the speed of the box?

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
01:31

Problem 116

In order to keep a leaking ship from sinking, it is necessary to pump $12 \mathrm{~kg}$ of water each second from below deck $2.1 \mathrm{~m}$ upward and over the side. What is the minimum horsepower motor that can be used to save the ship ( $1 \mathrm{hp}=746 \mathrm{~W})$ ?

Melissa Walsh
Melissa Walsh
Numerade Educator
01:42

Problem 117

Flight Human-powered aircraft require a pilot to pedal, as on bicycle, and to produce a sustained power output of about $0.30 \mathrm{hp}(1 \mathrm{hp}=746 \mathrm{~W})$. The Gossamer Albatross flew across the English Channel on June 12,1979 , in $2 \mathrm{~h} \mathrm{} 49 \mathrm{~min}$. (a) How much energy did the pilot expend during the flight? (b) How many candy bars (280 Cal per bar) would the pilot have to consume to be "fueled up" for the flight? Note that a nutritional calorie ( $1 \mathrm{Cal}$ ) is equivalent to 1000 calories ( $1000 \mathrm{cal}$ ) as defined in physics. In addition, the conversion factor between calories and joules is as follows: $1 \mathrm{Cal}=1000 \mathrm{cal}=1 \mathrm{kcal}=4186 \mathrm{~J} .$

James Kiss
James Kiss
Numerade Educator
03:52

Problem 118

A grandfather clock is powered by the descent of a $4.35-\mathrm{kg}$ weight. (a) If the weight descends through a distance of $0.760 \mathrm{~m}$ in $3.25$ days, how much power does it deliver to the clock? (b) To increase the power delivered to the clock, should the time it takes for the mass to descend be increased or decreased? Explain.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
07:34

Problem 119

To get out of bed in the morning, do you have to do work? Explain.

Sanat Mukherjee
Sanat Mukherjee
Numerade Educator
01:18

Problem 120

A leaf falls to the ground with constant speed. Is $P E_{i}+K E_{i}$ for this system greater than, less than, or equal to $P E_{f}+K E_{f}$ ? Explain.

Vysakh M
Vysakh M
Numerade Educator
01:39

Problem 121

A ball is dropped from rest. Which of the three graphs (A, B, or C) in Figure $6.15$ corresponds to (a) the potential energy, (b) the kinetic energy, and (c) the total mechanical energy for the ball as it falls to the ground? Assume that the system is ideal, with no form of friction.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
View

Problem 122

A spring has a spring constant of $310 \mathrm{~N} / \mathrm{m}$. Plot the potential energy for this spring when it is stretched by $1.0 \mathrm{~cm}, 2.0 \mathrm{~cm}, 3.0 \mathrm{~cm}$, and $4.0 \mathrm{~cm}$. Draw a curve that goes through your plotted points.

Gregory Devenport
Gregory Devenport
Numerade Educator
01:05

Problem 123

A small motor runs a lift that raises a load of bricks weighing $836 \mathrm{~N}$ to a height of $10.7 \mathrm{~m}$ in $23.2 \mathrm{~s}$. Assuming that the bricks are lifted with constant speed, what is the minimum power the motor must produce?

Eric Mockensturm
Eric Mockensturm
Numerade Educator
01:59

Problem 124

The human brain uses about $22 \mathrm{~W}$ of power under normal conditions (though more power may be required during exams!). How long can one Snickers bar (see Problem 117) power the normally functioning brain?

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
01:49

Problem 125

The Atmos clock (the so-called perpetual motion clock) gets its name from the fact that it runs off pressure variations in the atmosphere, which drive a bellows containing a mixture of gas and liquid ethyl chloride. Because the power to drive these clocks is so limited, they have to be very efficient. In fact, a single $60.0$-W lightbulb could power 240 million Atmos clocks simultaneously. Find the amount of energy, in joules, required to run an Atmos clock for 1 day.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
02:48

Problem 126

You push a $67-\mathrm{kg}$ box across a floor, where the coefficient of kinetic friction is $\mu_{\mathrm{k}}=0.55$. The force you exert is horizontal. How much power is needed to push the box at a speed of $0.50 \mathrm{~m} / \mathrm{s}$ ?

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
03:47

Problem 127

To clean a floor, a janitor pushes on a mop handle with a force of $43 \mathrm{~N}$. (a) If the mop handle is at an angle of $55^{\circ}$ above the horizontal, how much work is required to push the mop $0.50 \mathrm{~m}$ ? (b) If the angle the mop handle makes with the horizontal is increased to $65^{\circ}$, does the work done by the janitor increase, decrease, or stay the same? Explain.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
02:07

Problem 128

A small airplane tows a glider at constant speed and altitude. If the plane does $2.00 \times 10^{5} \mathrm{~J}$ of work to tow the glider $145 \mathrm{~m}$ and the tension in the tow rope is $2560 \mathrm{~N}$, what is the angle between the tow rope and the horizontal?

Nishant Kumar
Nishant Kumar
Numerade Educator
01:43

Problem 129

To make a batch of cookies, you mix half a bag of chocolate chips into a bowl of cookie dough, exerting a $21-\mathrm{N}$ force on the stirring spoon. Assume that your force is always in the direction of motion of the spoon. (a) What power is needed to move the spoon at a speed of $0.23 \mathrm{~m} / \mathrm{s}$ ? (b) How much work do you do if you stir the mixture for $1.5 \mathrm{~min}$ ?

Melissa Walsh
Melissa Walsh
Numerade Educator
01:42

Problem 130

A particle moves without friction. At point $A$ the particle has a kinetic energy of $12 \mathrm{~J}$; at point $B$ the particle is momentarily at rest, and the potential energy of the system is $25 \mathrm{~J}$; at point $\mathrm{C}$ the potential energy of the system is $5 \mathrm{~J}$. (a) What is the potential energy of the system when the particle is at point $A$ ? (b) What is the kinetic energy of the particle at point $\mathrm{C}$ ?

Melissa Walsh
Melissa Walsh
Numerade Educator
01:43

Problem 131

When a ball of mass $m$ is dropped from rest from a height $h$, its kinetic energy just before landing is KE. Now, suppose a second ball of mass $4 m$ is dropped from rest from a height $h / 4$. (a) Just before ball 2 lands, is its kinetic energy $4 K E, 2 K E, K E, K E / 2$, or $K E / 4$ ?
(b) Choose the best explanation from among the following:
A. The two balls have the same initial energy.
B. The more massive ball will have the greater kinetic energy.
C. The lower drop height results in a reduced kinetic energy.

James Kiss
James Kiss
Numerade Educator
03:32

Problem 132

On October 9, 1992, a 12-kg meteorite struck a car in Peekskill, New York, creating a dent about $22 \mathrm{~cm}$ deep, as shown in Figure 6.16. If the initial speed of the meteorite was $550 \mathrm{~m} / \mathrm{s}$, what was the average force exerted on the meteorite by the car?

Hubert Agamasu
Hubert Agamasu
Numerade Educator
02:22

Problem 133

(a) At what rate must you lift a $3.6-\mathrm{kg}$ container of milk (1 gallon) if the power output of your arm is to be $22 \mathrm{~W}$ ?
(b) How long does it take to lift the milk container through a distance of $1.0 \mathrm{~m}$ at this rate?

Melissa Walsh
Melissa Walsh
Numerade Educator
02:34

Problem 134

A catapult launcher on aircraft carrier accelerates a jet from rest to $72 \mathrm{~m} / \mathrm{s}$. The work done by the catapult during the launch is $7.6 \times 10^{7} \mathrm{~J}$. (a) What is the mass of the jet? (b) If the jet is in contact with the catapult for $2.0 \mathrm{~s}$, what is the power output of the catapult?

Nishant Kumar
Nishant Kumar
Numerade Educator
01:55

Problem 135

The water skier in Figure $6.11$ is at an angle of $35^{\circ}$ with respect to the center line of the boat and is being pulled at a constant speed of $14 \mathrm{~m} / \mathrm{s}$. (a) If the tension in the tow rope is $90.0 \mathrm{~N}$, how much work does the rope do on the skier in $10.0 \mathrm{~s}$ ? (b) How much work does the resistive force of water do on the skier in the same time?

James Kiss
James Kiss
Numerade Educator
03:18

Problem 136

Calculate the power output of a $1.8$-g spider as it walks up a windowpane at $2.3 \mathrm{~cm} / \mathrm{s}$. The spider walks on a path that is at $25^{\circ}$ to the vertical, as illustrated in Figure 6.17.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
03:25

Problem 137

A pitcher accelerates a $0.14-\mathrm{kg}$ hardball from rest to $25.5 \mathrm{~m} / \mathrm{s}$ in $0.075 \mathrm{~s}$. (a) How much work does the pitcher do on the ball? (b) What is the pitcher's power output during the pitch? (c) Suppose the ball reaches $25.5 \mathrm{~m} / \mathrm{s}$ in less than $0.075 \mathrm{~s}$. Is the power produced by the pitcher in this case more than, less than, or the same as the power found in part (b)? Explain.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
03:36

Problem 138

The average power output of the human heart is $1.33 \mathrm{~W}$. (a) How much energy does the heart produce in a day? (b) Compare the energy found in part (a) with the energy required to walk up a flight of stairs. Estimate the height a person could attain on a set of stairs using nothing more than the daily energy produced by the heart.

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
04:30

Problem 139

A sled slides without friction down a small, ice-covered hill. If the sled starts from rest at the top of the hill, its speed at the bottom is $7.50 \mathrm{~m} / \mathrm{s}$. (a) On a second run, the sled starts with a speed of $1.50 \mathrm{~m} / \mathrm{s}$ at the top. When it reaches the bottom of the hill, is its speed $9.00 \mathrm{~m} / \mathrm{s}$, more than $9.00 \mathrm{~m} / \mathrm{s}$, or less than $9.00 \mathrm{~m} / \mathrm{s}$ ? Explain. (b) Find the speed of the sled at the bottom of the hill after the second run.

Khoobchandra Agrawal
Khoobchandra Agrawal
Numerade Educator
02:13

Problem 140

An $1865-\mathrm{kg}$ airplane starts at rest on an airport runway at sea level. What is the change in mechanical energy of the airplane if it climbs to a cruising altitude of $2420 \mathrm{~m}$ and maintains a constant speed of $96.5 \mathrm{~m} / \mathrm{s}$ ?

Nishant Kumar
Nishant Kumar
Numerade Educator
04:42

Problem 141

The water slide shown in Figure $6.18$ ends at a height of $1.50 \mathrm{~m}$ above the pool. If the person starts from rest at point $\mathrm{A}$ and lands in the water at point $\mathrm{B}$, what is the height $h$ of the water slide? (Assume that the water slide is frictionless.)

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
02:27

Problem 142

A skateboarder starts at point $\mathrm{A}$ in Figure 6.19 and rises to a height of $2.64 \mathrm{~m}$ above the top of the ramp at point $B$. What was the skateboarder's initial speed at point A?

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
02:36

Problem 143

A 1.9-kg block slides down a frictionless ramp, as shown in Figure 6.20. The top of the ramp is $1.5 \mathrm{~m}$ above the ground; the bottom of the ramp is $0.25 \mathrm{~m}$ above the ground. The block leaves the ramp moving horizontally, and lands a horizontal distance $d$ away. Find the distance $d$.

Khoobchandra Agrawal
Khoobchandra Agrawal
Numerade Educator
01:37

Problem 144

Research and write a report on the power that humans produce in everyday life. Include the power produced by the brain when thinking and the heart when resting. Also select several strenuous activities such as trackand-field events, bicycle racing, and swimming. In each case, explain how the power is determined. Make a table to compare the various power outputs.

Dominador Tan
Dominador Tan
Numerade Educator
View

Problem 145

Connect to the Big Idea The mechanical energy of a falling ball stays the same, even though it is constantly speeding up. Similarly, if you throw a ball upward, it slows down, even though its mechanical energy stays the same. Explain.

Gregory Devenport
Gregory Devenport
Numerade Educator
01:51

Problem 146

Estimate the range of flight speeds for Microraptor gui if its power output is $9.8 \mathrm{~W}$.
A. $0-7.7 \mathrm{~m} / \mathrm{s}$
C. $15-30 \mathrm{~m} / \mathrm{s}$
B. $7.7-15 \mathrm{~m} / \mathrm{s}$
D. $0-15 \mathrm{~m} / \mathrm{s}$

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
01:38

Problem 147

What approximate range of flight speeds would be possible if Microraptor gui could produce $20 \mathrm{~W}$ of power?
A. $0-25 \mathrm{~m} / \mathrm{s}$
C. $2.5-25 \mathrm{~m} / \mathrm{s}$
B. $25-30 \mathrm{~m} / \mathrm{s}$
D. $0-2.5 \mathrm{~m} / \mathrm{s}$

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator
01:43

Problem 148

How much energy would Microraptor gui have to expend to fly with a speed of $10 \mathrm{~m} / \mathrm{s}$ for $1.0 \mathrm{~min}$ ?
A. $8.1 \mathrm{~J}$
C. $490 \mathrm{~J}$
B. $81 \mathrm{~J}$
D. $600 \mathrm{~J}$

Prabhakar Kumar
Prabhakar Kumar
Numerade Educator