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University Physics Volume 1

Samuel J. Ling, Jeff Sanny, William Moebs

Chapter 5

Newton's Laws of Motion - all with Video Answers

Educators

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Chapter Questions

02:54

Problem 1

What properties do forces have that allow us to classify them as vectors?

Linda Winkler
Linda Winkler
Numerade Educator
06:39

Problem 2

Taking a frame attached to Earth as inertial, which of the following objects cannot have inertial frames attached to them, and which are inertial reference frames?
(a) A car moving at constant velocity
(b) A car that is accelerating
(c) An elevator in free fall
(d) A space capsule orbiting Earth
(e) An elevator descending uniformly

Linda Winkler
Linda Winkler
Numerade Educator
02:33

Problem 3

A woman was transporting an open box of cupcakes to a school party. The car in front of her stopped suddenly; she applied her brakes immediately. She was wearing her seat belt and suffered no physical harm (just a great deal of embarrassment), but the cupcakes flew into the dashboard and became "smushcakes." Explain what happened.

Linda Winkler
Linda Winkler
Numerade Educator
04:44

Problem 4

Why can we neglect forces such as those holding a body together when we apply Newton's second law?

Linda Winkler
Linda Winkler
Numerade Educator
02:40

Problem 5

A rock is thrown straight up. At the top of the trajectory, the velocity is momentarily zero. Does this imply that the force acting on the object is zero? Explain your answer.

Linda Winkler
Linda Winkler
Numerade Educator
04:07

Problem 6

What is the relationship between weight and mass? Which is an intrinsic, unchanging property of a body?

Linda Winkler
Linda Winkler
Numerade Educator
04:09

Problem 7

How much does a 70 -kg astronaut weight in space, far from any celestial body? What is her mass at this location?

Linda Winkler
Linda Winkler
Numerade Educator
05:12

Problem 8

Which of the following statements is accurate?
(a) Mass and weight are the same thing expressed in different units.
(b) If an object has no weight, it must have no mass.
(c) If the weight of an object varies, so must the mass.
(d) Mass and inertia are different concepts.
(e) Weight is always proportional to mass.

Linda Winkler
Linda Winkler
Numerade Educator
04:28

Problem 9

When you stand on Earth, your feet push against it with a force equal to your weight. Why doesn't Earth accelerate away from you?

Linda Winkler
Linda Winkler
Numerade Educator
02:37

Problem 10

How would you give the value of $\overrightarrow{\mathrm{g}}$ in vector form?

Linda Winkler
Linda Winkler
Numerade Educator
01:19

Problem 11

Identify the action and reaction forces in the following

Vasu Makani
Vasu Makani
Numerade Educator
09:35

Problem 11

Identify the action and reaction forces in the following situations: (a) Earth attracts the Moon, (b) a boy kicks a football, (c) a rocket accelerates upward, (d) a car accelerates forward, (e) a high jumper leaps, and (f) a bullet is shot from a gun.

Linda Winkler
Linda Winkler
Numerade Educator
01:36

Problem 12

Suppose that you are holding a cup of coffee in your hand. Identify all forces on the cup and the reaction to each force.

Darshan Maheshwari
Darshan Maheshwari
Numerade Educator
02:06

Problem 13

(a) Why does an ordinary rifle recoil (kick backward) when fired? (b) The barrel of a recoilless rifle is open at both ends. Describe how Newton's third law applies when one is fired. (c) Can you safely stand close behind one when it is fired?

Surjit Tewari
Surjit Tewari
Numerade Educator
02:21

Problem 14

A table is placed on a rug. Then a book is placed on the table. What does the floor exert a normal force on?

Linda Winkler
Linda Winkler
Numerade Educator
02:00

Problem 15

A particle is moving to the right. (a) Can the force on it be acting to the left? If yes, what would happen? (b) Can that force be acting downward? If yes, why?15. A particle is moving to the right. (a) Can the force on it be acting to the left? If yes, what would happen? (b) Can that force be acting downward? If yes, why?

Surjit Tewari
Surjit Tewari
Numerade Educator
01:56

Problem 16

In completing the solution for a problem involving forces, what do we do after constructing the free-body diagram? That is, what do we apply?

Linda Winkler
Linda Winkler
Numerade Educator
01:20

Problem 17

If a book is located on a table, how many forces should be shown in a free-body diagram of the book? Describe them.

Linda Winkler
Linda Winkler
Numerade Educator
01:58

Problem 18

If the book in the previous question is in free fall, how many forces should be shown in a free-body diagram of the book? Describe them.

Linda Winkler
Linda Winkler
Numerade Educator
01:43

Problem 19

Two ropes are attached to a tree, and forces of $\overrightarrow{\mathbf{F}}_{1}=2.0 \hat{\mathbf{i}}+4.0 \hat{\mathbf{j}} \mathrm{N} \quad$ and $\quad \overrightarrow{\mathbf{F}}_{2}=3.0 \hat{\mathbf{i}}+6.0 \hat{\mathbf{j}} \mathrm{N}$
are applied. The forces are coplanar (in the same plane). (a) What is the resultant (net force) of these two force vectors?
(b) Find the magnitude and direction of this net force.

Surjit Tewari
Surjit Tewari
Numerade Educator
02:11

Problem 20

A telephone pole has three cables pulling as shown from above, with $\quad \overrightarrow{\mathbf{F}}_{1}=(300.0 \hat{\mathbf{i}}+500.0 \hat{\mathbf{j}})$
$\overrightarrow{\mathbf{F}}_{2}=-200.0 \hat{\mathbf{i}},$ and $\quad \overrightarrow{\mathbf{F}}_{3}=-800.0 \hat{\mathbf{j}} .$ (a) Find the
net force on the telephone pole in component form. (b) Find the magnitude and direction of this net force.

Manish Kumar ( Iit K )
Manish Kumar ( Iit K )
Numerade Educator
06:43

Problem 21

Two teenagers are pulling on ropes attached to a tree. The angle between the ropes is $30.0^{\circ} .$ David pulls with a force of $400.0 \mathrm{N}$ and Stephanie pulls with a force of 300.0 N. (a) Find the component form of the net force. (b) Find the magnitude of the resultant (net) force on the tree and the angle it makes with David's rope.

Linda Winkler
Linda Winkler
Numerade Educator
02:02

Problem 22

Two forces of $\overrightarrow{\mathbf{F}}_{1}=\frac{75.0}{\sqrt{2}}(\hat{\mathbf{i}}-\hat{\mathbf{j}}) \mathrm{N} \quad$ and
$\overrightarrow{\mathbf{F}}_{2}=\frac{150.0}{\sqrt{2}}(\hat{\mathbf{i}}-\hat{\mathbf{j}}) \mathrm{N}$ act on an object. Find the third
force $\overrightarrow{\mathbf{F}}_{3}$ that is needed to balance the first two forces.

Vishal Gupta
Vishal Gupta
Numerade Educator
04:15

Problem 23

While sliding a couch across a floor, Andrea and Jennifer exert forces $\overrightarrow{\mathbf{F}}_{\mathrm{A}}$ and $\overrightarrow{\mathbf{F}}_{\mathbf{J}}$ on the couch. Andrea's force is due north with a magnitude of $130.0 \mathrm{N}$ and Jennifer's force is $32^{\circ}$ east of north with a magnitude of $180.0 \mathrm{N}$. (a) Find the net force in component form. (b) Find the magnitude and direction of the net force. (c) If Andrea and Jennifer's housemates, David and Stephanie, disagree with the move and want to prevent its relocation, with what combined force $\overrightarrow{\mathbf{F}}$ DS should they push so that the couch does not move?

Surjit Tewari
Surjit Tewari
Numerade Educator
02:36

Problem 24

Andrea, a 63.0-kg sprinter, starts a race with an acceleration of $4.200 \mathrm{m} / \mathrm{s}^{2}$. What is the net external force on her?

Linda Winkler
Linda Winkler
Numerade Educator
06:59

Problem 25

If the sprinter from the previous problem accelerates at that rate for $20.00 \mathrm{m}$ and then maintains that velocity for the remainder of a 100.00 -m dash, what will her time be for the race?

Linda Winkler
Linda Winkler
Numerade Educator
02:38

Problem 26

A cleaner pushes a 4.50-kg laundry cart in such a way that the net external force on it is $60.0 \mathrm{N}$. Calculate the magnitude of his cart's acceleration.

Linda Winkler
Linda Winkler
Numerade Educator
02:54

Problem 27

Astronauts in orbit are apparently weightless. This means that a clever method of measuring the mass of astronauts is needed to monitor their mass gains or losses, and adjust their diet. One way to do this is to exert a known force on an astronaut and measure the acceleration produced. Suppose a net external force of $50.0 \mathrm{N}$ is exerted, and an astronaut's acceleration is measured to be $0.893 \mathrm{m} / \mathrm{s}^{2} .$ (a) Calculate her mass. (b) By exerting a force on the astronaut, the vehicle in which she orbits experiences an equal and opposite force. Use this knowledge to find an equation for the acceleration of the system (astronaut and spaceship) that would be measured by a nearby observer. (c) Discuss how this would affect the measurement of the astronaut's acceleration. Propose a method by which recoil of the vehicle is avoided.

Surjit Tewari
Surjit Tewari
Numerade Educator
07:22

Problem 28

In Figure $5.12,$ the net external force on the $24-\mathrm{kg}$ mower is given as 51 N. If the force of friction opposing the motion is $24 \mathrm{N},$ what force $F$ (in newtons) is the person exerting on the mower? Suppose the mower is moving at $1.5 \mathrm{m} / \mathrm{s}$ when the force $F$ is removed. How far will the mower go before stopping?

Linda Winkler
Linda Winkler
Numerade Educator
02:47

Problem 29

The rocket sled shown below decelerates at a rate of $196 \mathrm{m} / \mathrm{s}^{2}$. What force is necessary to produce this deceleration? Assume that the rockets are off. The mass of the system is $2.10 \times 10^{3} \mathrm{kg}.$

Linda Winkler
Linda Winkler
Numerade Educator
01:23

Problem 30

If the rocket sled shown in the previous problem starts with only one rocket burning, what is the magnitude of this acceleration? Assume that the mass of the system is $2.10 \times 10^{3} \mathrm{kg},$ the thrust $T$ is $2.40 \times 10^{4} \mathrm{N},$ and the force of friction opposing the motion is $650.0 \mathrm{N}$. (b) Why is the acceleration not one-fourth of what it is with all rockets burning?

Surjit Tewari
Surjit Tewari
Numerade Educator
03:21

Problem 31

What is the deceleration of the rocket sled if it comes to rest in $1.10 \mathrm{s}$ from a speed of $1000.0 \mathrm{km} / \mathrm{h}$ ? (Such deceleration caused one test subject to black out and have temporary blindness.)

Linda Winkler
Linda Winkler
Numerade Educator
02:21

Problem 32

Suppose two children push horizontally, but in exactly opposite directions, on a third child in a wagon. The first child exerts a force of $75.0 \mathrm{N},$ the second exerts a force of $90.0 \mathrm{N},$ friction is $12.0 \mathrm{N},$ and the mass of the third child plus wagon is $23.0 \mathrm{kg}$. (a) What is the system of interest if the acceleration of the child in the wagon is to be calculated? (See the free-body diagram.) (b) Calculate the acceleration. (c) What would the acceleration be if friction were 15.0 N?

Surjit Tewari
Surjit Tewari
Numerade Educator
04:06

Problem 33

A powerful motorcycle can produce an acceleration of $3.50 \mathrm{m} / \mathrm{s}^{2}$ while traveling at $90.0 \mathrm{km} / \mathrm{h}$. At that speed, the forces resisting motion, including friction and air resistance, total 400.0 N. (Air resistance is analogous to air friction. It always opposes the motion of an object.) What is the magnitude of the force that motorcycle exerts backward on the ground to produce its acceleration if the mass of the motorcycle with rider is $245 \mathrm{kg} ?$

Coleen Amado
Coleen Amado
Numerade Educator
03:37

Problem 34

A car with a mass of $1000.0 \mathrm{kg}$ accelerates from 0 to $90.0 \mathrm{km} / \mathrm{h}$ in $10.0 \mathrm{s}$. (a) What is its acceleration? (b) What is the net force on the car?

Linda Winkler
Linda Winkler
Numerade Educator
04:48

Problem 35

The driver in the previous problem applies the brakes when the car is moving at $90.0 \mathrm{km} / \mathrm{h}$, and the car comes to rest after traveling 40.0 $\mathrm{m}$. What is the net force on the car during its deceleration?

Linda Winkler
Linda Winkler
Numerade Educator
View

Problem 36

An 80.0-kg passenger in an SUV traveling at $1.00 \times 10^{3} \mathrm{km} / \mathrm{h}$ is wearing a seat belt. The driver slams on the brakes and the SUV stops in $45.0 \mathrm{m}$. Find the force of the seat belt on the passenger.

Ankur S
Ankur S
Numerade Educator
04:50

Problem 37

A particle of mass 2.0 kg is acted on by a single force
$\overrightarrow{\mathbf{F}}_{1}=18 \hat{\mathbf{i}} \mathrm{N} .$ (a) What is the particle's acceleration? (b) If the particle starts at rest, how far does it travel in the first $5.0 \mathrm{s} ?$

Linda Winkler
Linda Winkler
Numerade Educator
02:52

Problem 38

Suppose that the particle of the previous problem also experiences forces $\overrightarrow{\mathbf{F}}_{2}=-15 \hat{\mathbf{i}} \mathbf{N} \quad$ and
$\overrightarrow{\mathbf{F}}_{3}=6.0 \hat{\mathbf{j}} \mathrm{N} .$ What is its acceleration in this case?

Surjit Tewari
Surjit Tewari
Numerade Educator
02:06

Problem 39

Find the acceleration of the body of mass $5.0 \mathrm{kg}$ shown below.

Nishant Kumar
Nishant Kumar
Numerade Educator
01:56

Problem 40

In the following figure, the horizontal surface on which this block slides is frictionless. If the two forces acting on it each have magnitude $F=30.0 \mathrm{N}$ and $M=10.0 \mathrm{kg},$ what is the magnitude of the resulting
acceleration of the block?

Surjit Tewari
Surjit Tewari
Numerade Educator
03:41

Problem 41

The weight of an astronaut plus his space suit on the Moon is only 250 N. (a) How much does the suited astronaut weigh on Earth? (b) What is the mass on the Moon? On Earth?

Linda Winkler
Linda Winkler
Numerade Educator
02:23

Problem 42

Suppose the mass of a fully loaded module in which astronauts take off from the Moon is $1.00 \times 10^{4}$ kg. The thrust of its engines is $3.00 \times 10^{4}$ N. (a) Calculate the module's magnitude of acceleration in a vertical takeoff from the Moon. (b) Could it lift off from Earth? If not, why not? If it could, calculate the magnitude of its acceleration.

Surjit Tewari
Surjit Tewari
Numerade Educator
07:33

Problem 43

A rocket sled accelerates at a rate of $49.0 \mathrm{m} / \mathrm{s}^{2}$
Its passenger has a mass of $75.0 \mathrm{kg}$. (a) Calculate the horizontal component of the force the seat exerts against his body. Compare this with his weight using a ratio. (b) Calculate the direction and magnitude of the total force the seat exerts against his body.

Linda Winkler
Linda Winkler
Numerade Educator
07:51

Problem 44

Repeat the previous problem for a situation in which the rocket sled decelerates at a rate of $201 \mathrm{m} / \mathrm{s}^{2}$. In this problem, the forces are exerted by the seat and the seat belt.

Linda Winkler
Linda Winkler
Numerade Educator
04:10

Problem 45

A body of mass 2.00 kg is pushed straight upward by a 25.0 N vertical force. What is its acceleration?

Linda Winkler
Linda Winkler
Numerade Educator
02:41

Problem 46

A car weighing 12,500 N starts from rest and accelerates to $83.0 \mathrm{km} / \mathrm{h}$ in $5.00 \mathrm{s}$. The friction force is 1350 N. Find the applied force produced by the engine.

Supratim Pal
Supratim Pal
Numerade Educator
02:58

Problem 47

A body with a mass of $10.0 \mathrm{kg}$ is assumed to be in Earth's gravitational field with $g=9.80 \mathrm{m} / \mathrm{s}^{2} .$ What is its acceleration?

Linda Winkler
Linda Winkler
Numerade Educator
01:16

Problem 48

A fireman has mass $m$; he hears the fire alarm and slides down the pole with acceleration $a$ (which is less than $g$ in magnitude). (a) Write an equation giving the vertical force he must apply to the pole. (b) If his mass is $90.0 \mathrm{kg}$ and he accelerates at $5.00 \mathrm{m} / \mathrm{s}^{2},$ what is the magnitude of his applied force?

Surjit Tewari
Surjit Tewari
Numerade Educator
06:02

Problem 49

A baseball catcher is performing a stunt for a television commercial. He will catch a baseball (mass 145 g) dropped from a height of $60.0 \mathrm{m}$ above his glove. His glove stops the ball in 0.0100 s. What is the force exerted by his glove on the ball?

Linda Winkler
Linda Winkler
Numerade Educator
02:44

Problem 50

When the Moon is directly overhead at sunset, the force by Earth on the Moon, $F_{\mathrm{EM}},$ is essentially at $90^{\circ}$ to the force by the Sun on the Moon, $F_{\mathrm{SM}},$ as shown below. Given that $F_{\mathrm{EM}}=1.98 \times 10^{20} \mathrm{N} \quad$ and $F_{\mathrm{SM}}=4.36 \times 10^{20} \mathrm{N}, \quad$ all other forces on the Moon are negligible, and the mass of the Moon is $7.35 \times 10^{22} \mathrm{kg}$ determine the magnitude of the Moon's acceleration.

Surjit Tewari
Surjit Tewari
Numerade Educator
03:51

Problem 51

(a) What net external force is exerted on a $1100.0-\mathrm{kg}$ artillery shell fired from a battleship if the shell is accelerated at $2.40 \times 10^{4} \mathrm{m} / \mathrm{s}^{2} ?$ (b) What is the magnitude of the force exerted on the ship by the artillery shell, and why?

Linda Winkler
Linda Winkler
Numerade Educator
02:17

Problem 52

A brave but inadequate rugby player is being pushed backward by an opposing player who is exerting a force of $800.0 \mathrm{N}$ on him. The mass of the losing player plus equipment is $90.0 \mathrm{kg}$, and he is accelerating backward at $1.20 \mathrm{m} / \mathrm{s}^{2} .$ (a) What is the force of friction between the losing player's feet and the grass? (b) What force does the winning player exert on the ground to move forward if his mass plus equipment is $110.0 \mathrm{kg}$ ?

Surjit Tewari
Surjit Tewari
Numerade Educator
03:26

Problem 53

A history book is lying on top of a physics book on a desk, as shown below; a free-body diagram is also shown. The history and physics books weigh $14 \mathrm{N}$ and 18 N, respectively. Identify each force on each book with a double subscript notation (for instance, the contact force of the history book pressing against physics book can be described as $\overrightarrow{\mathbf{F}}_{\mathrm{HP}}$ ), and determine the value of each of these forces, explaining the process used.

Surjit Tewari
Surjit Tewari
Numerade Educator
03:48

Problem 54

A truck collides with a car, and during the collision, the net force on each vehicle is essentially the force exerted by the other. Suppose the mass of the car is $550 \mathrm{kg}$, the mass of the truck is $2200 \mathrm{kg}$, and the magnitude of the truck's acceleration is $10 \mathrm{m} / \mathrm{s}^{2}$. Find the magnitude of the car's acceleration.

Linda Winkler
Linda Winkler
Numerade Educator
01:35

Problem 55

A leg is suspended in a traction system, as shown below. (a) Which pulley in the figure is used to calculate the force exerted on the foot? (b) What is the tension in the rope? Here $\overrightarrow{\mathbf{T}}$ is the tension, $\overrightarrow{\mathbf{w}}$ leg is the weight of the leg, and $\overrightarrow{\boldsymbol{w}}$ is the weight of the load that provides the tension.

Surjit Tewari
Surjit Tewari
Numerade Educator
01:22

Problem 56

Suppose the shinbone in the preceding image was a femur in a traction setup for a broken bone, with pulleys and rope available. How might we be able to increase the force along the femur using the same weight?

Surjit Tewari
Surjit Tewari
Numerade Educator
02:35

Problem 57

Two teams of nine members each engage in tug-ofwar. Each of the first team's members has an average mass of $68 \mathrm{kg}$ and exerts an average force of $1350 \mathrm{N}$ horizontally. Each of the second team's members has an average mass of 73 kg and exerts an average force of 1365 N horizontally. (a) What is magnitude of the acceleration of the two teams, and which team wins? (b) What is the tension in the section of rope between the teams?

Surjit Tewari
Surjit Tewari
Numerade Educator
03:42

Problem 58

What force does a trampoline have to apply to Jennifer, a 45.0-kg gymnast, to accelerate her straight up at $7.50 \mathrm{m} / \mathrm{s}^{2}$ ? The answer is independent of the velocity of the gymnast-she can be moving up or down or can be instantly stationary.

Linda Winkler
Linda Winkler
Numerade Educator
02:27

Problem 59

(a) Calculate the tension in a vertical strand of spider web if a spider of mass $2.00 \times 10^{-5} \mathrm{kg}$ hangs motionless on it. (b) Calculate the tension in a horizontal strand of spider web if the same spider sits motionless in the middle of it much like the tightrope walker in Figure $5.26 .$ The strand sags at an angle of $12^{\circ}$ below the horizontal. Compare this with the tension in the vertical strand (find their ratio).

Surjit Tewari
Surjit Tewari
Numerade Educator
01:28

Problem 60

Suppose Kevin, a 60.0-kg gymnast, climbs a rope. (a) What is the tension in the rope if he climbs at a constant speed? (b) What is the tension in the rope if he accelerates upward at a rate of $1.50 \mathrm{m} / \mathrm{s}^{2} ?$

Surjit Tewari
Surjit Tewari
Numerade Educator
05:09

Problem 61

Show that, as explained in the text, a force $F_{\perp}$ Bexerted on a flexible medium at its center and perpendicular to its length (such as on the tightrope wire in Figure 5.26 )

Linda Winkler
Linda Winkler
Numerade Educator
01:16

Problem 62

Consider Figure 5.28. The driver attempts to get the car out of the mud by exerting a perpendicular force of 610.0 N, and the distance she pushes in the middle of the rope is $1.00 \mathrm{m}$ while she stands $6.00 \mathrm{m}$ away from the car on the left and $6.00 \mathrm{m}$ away from the tree on the right. What is the tension $T$ in the rope, and how do you find the answer?

Surjit Tewari
Surjit Tewari
Numerade Educator
01:57

Problem 63

A bird has a mass of 26 g and perches in the middle of a stretched telephone line. (a) Show that the tension in the line can be calculated using the equation $T=\frac{m g}{2 \sin \theta}$
Determine the tension when (b) $\theta=5^{\circ}$ and (c) $\theta=0.5^{\circ}$ Assume that each half of the line is straight.

Surjit Tewari
Surjit Tewari
Numerade Educator
01:47

Problem 64

One end of a $30-\mathrm{m}$ rope is tied to a tree; the other end is tied to a car stuck in the mud. The motorist pulls sideways on the midpoint of the rope, displacing it a distance of $2 \mathrm{m}$. If he exerts a force of $80 \mathrm{N}$ under these conditions, determine the force exerted on the car.

Surjit Tewari
Surjit Tewari
Numerade Educator
02:50

Problem 65

Consider the baby being weighed in the following figure. (a) What is the mass of the infant and basket if a scale reading of $55 \mathrm{N}$ is observed? (b) What is tension $T_{1}$ in the cord attaching the baby to the scale? (c) What is tension $T_{2}$ in the cord attaching the scale to the ceiling, if the scale has a mass of $0.500 \mathrm{kg}$ ? (d) Sketch the situation, indicating the system of interest used to solve each part. The masses of the cords are negligible.

Surjit Tewari
Surjit Tewari
Numerade Educator
02:36

Problem 66

What force must be applied to a 100.0 -kg crate on a frictionless plane inclined at $30^{\circ}$ to cause an acceleration of $2.0 \mathrm{m} / \mathrm{s}^{2}$ up the plane?

Surjit Tewari
Surjit Tewari
Numerade Educator
03:19

Problem 67

A 2.0-kg block is on a perfectly smooth ramp that makes an angle of $30^{\circ}$ with the horizontal. (a) What is the block's acceleration down the ramp and the force of the ramp on the block? (b) What force applied upward along and parallel to the ramp would allow the block to move with constant velocity?

Surjit Tewari
Surjit Tewari
Numerade Educator
00:51

Problem 68

A ball of mass $m$ hangs at rest, suspended by a string. (a) Sketch all forces. (b) Draw the free-body diagram for the ball.

Surjit Tewari
Surjit Tewari
Numerade Educator
03:30

Problem 69

A car moves along a horizontal road. Draw a free-body diagram; be sure to include the friction of the road that opposes the forward motion of the car.

Linda Winkler
Linda Winkler
Numerade Educator
01:05

Problem 70

A runner pushes against the track, as shown. (a) Provide a free-body diagram showing all the forces on the runner. (Hint: Place all forces at the center of his body, and include his weight.) (b) Give a revised diagram showing the xy-component form.

Surjit Tewari
Surjit Tewari
Numerade Educator
05:10

Problem 71

The traffic light hangs from the cables as shown. Draw a free-body diagram on a coordinate plane for this situation.

Linda Winkler
Linda Winkler
Numerade Educator
04:21

Problem 72

Two small forces, $\overrightarrow{\mathbf{F}}_{1}=-2.40 \hat{\mathbf{i}}-6.10 t \hat{\mathbf{j}}$ N and $\overrightarrow{\mathbf{F}}_{2}=8.50 \hat{\mathbf{i}}-9.70 \hat{\mathbf{j}} \quad \mathrm{N},$ are exerted on a rogue asteroid by a pair of space tractors. (a) Find the net force.
(b) What are the magnitude and direction of the net force?
(c) If the mass of the asteroid is 125 kg, what acceleration does it experience (in vector form)? (d) What are the magnitude and direction of the acceleration?

Surjit Tewari
Surjit Tewari
Numerade Educator
05:53

Problem 73

Two forces of 25 and 45 N act on an object. Their directions differ by $70^{\circ} .$ The resulting acceleration has magnitude of $10.0 \mathrm{m} / \mathrm{s}^{2}$. What is the mass of the body?

Linda Winkler
Linda Winkler
Numerade Educator
02:24

Problem 74

A force of $1600 \mathrm{N}$ acts parallel to a ramp to push a 300-kg piano into a moving van. The ramp is inclined at $20^{\circ} .$ (a) What is the acceleration of the piano up the ramp? (b) What is the velocity of the piano when it reaches the top if the ramp is $4.0 \mathrm{m}$ long and the piano starts from rest?

Surjit Tewari
Surjit Tewari
Numerade Educator
02:05

Problem 75

Draw a free-body diagram of a diver who has entered the water, moved downward, and is acted on by an upward force due to the water which balances the weight (that is, the diver is suspended).

Linda Winkler
Linda Winkler
Numerade Educator
02:16

Problem 76

For a swimmer who has just jumped off a diving board, assume air resistance is negligible. The swimmer has a mass of $80.0 \mathrm{kg}$ and jumps off a board $10.0 \mathrm{m}$ above the water. Three seconds after entering the water, her downward motion is stopped. What average upward force did the water exert on her?

Supratim Pal
Supratim Pal
Numerade Educator
01:45

Problem 77

(a) Find an equation to determine the magnitude of the net force required to stop a car of mass $m,$ given that the initial speed of the car is $v_{0}$ and the stopping distance is $x.$
(b) Find the magnitude of the net force if the mass of the car is $1050 \mathrm{kg}$, the initial speed is $40.0 \mathrm{km} / \mathrm{h}$, and the stopping distance is $25.0 \mathrm{m}$.

Surjit Tewari
Surjit Tewari
Numerade Educator
03:43

Problem 78

A sailboat has a mass of $1.50 \times 10^{3} \mathrm{kg}$ and is acted on by a force of $2.00 \times 10^{3} \mathrm{N}$ toward the east, while the wind acts behind the sails with a force of $3.00 \times 10^{3} \mathrm{N}$ in a direction $45^{\circ}$ north of east. Find the magnitude and direction of the resulting acceleration.

Surjit Tewari
Surjit Tewari
Numerade Educator
03:58

Problem 79

Find the acceleration of the body of mass $10.0 \mathrm{kg}$ shown below.

Surjit Tewari
Surjit Tewari
Numerade Educator
05:41

Problem 80

A body of mass 2.0 kg is moving along the $x$ -axis with a speed of $3.0 \mathrm{m} / \mathrm{s}$ at the instant represented below. (a) What is the acceleration of the body? (b) What is the body's velocity 10.0 s later? (c) What is its displacement after 10.0 s?

Supratim Pal
Supratim Pal
Numerade Educator
02:46

Problem 81

Force $\overrightarrow{\mathbf{F}}$ s has twice the magnitude of force $\overrightarrow{\mathbf{F}}$ A. Find the direction in which the particle accelerates in this figure.

Surjit Tewari
Surjit Tewari
Numerade Educator
13:27

Problem 82

Shown below is a body of mass $1.0 \mathrm{kg}$ under the influence of the forces $\overrightarrow{\mathbf{F}}_{\mathbf{A}}, \overrightarrow{\mathbf{F}}_{\mathbf{B}},$ and $m \overrightarrow{\mathbf{g}}$. If the body accelerates to the left at $20 \mathrm{m} / \mathrm{s}^{2},$ what are $\overrightarrow{\mathbf{F}}_{\mathbf{A}}$ and $\overrightarrow{\mathbf{F}}_{\mathbf{B}} ?$

Yaqub Khan
Yaqub Khan
Numerade Educator
02:05

Problem 83

A force acts on a car of mass $m$ so that the speed $v$ of the car increases with position $x$ as $v=k x^{2},$ where $k$ is constant and all quantities are in SI units. Find the force acting on the car as a function of position.

Surjit Tewari
Surjit Tewari
Numerade Educator
02:08

Problem 84

A 7.0-N force parallel to an incline is applied to a 1.0-kg crate. The ramp is tilted at $20^{\circ}$ and is frictionless. (a) What is the acceleration of the crate? (b) If all other conditions are the same but the ramp has a friction force of 1.9 $\mathrm{N},$ what is the acceleration?

Surjit Tewari
Surjit Tewari
Numerade Educator
02:01

Problem 85

Two boxes, A and B, are at rest. Box A is on level ground, while box $\mathrm{B}$ rests on an inclined plane tilted at angle $\theta$ with the horizontal. (a) Write expressions for the normal force acting on each block. (b) Compare the two forces; that is, tell which one is larger or whether they are equal in magnitude. (c) If the angle of incline is $10^{\circ},$ which force is greater?

Surjit Tewari
Surjit Tewari
Numerade Educator
04:44

Problem 86

A mass of 250.0 g is suspended from a spring hanging vertically. The spring stretches $6.00 \mathrm{cm} .$ How much will the spring stretch if the suspended mass is $530.0 \mathrm{g}$ ?

Linda Winkler
Linda Winkler
Numerade Educator
01:41

Problem 87

As shown below, two identical springs, each with the spring constant 20 $\mathrm{N} / \mathrm{m},$ support a 15.0 -N weight. (a) What is the tension in spring $\mathrm{A}$ ? (b) What is the amount of stretch of spring A from the rest position?

Surjit Tewari
Surjit Tewari
Numerade Educator
02:09

Problem 88

Shown below is a 30.0-kg block resting on a frictionless ramp inclined at $60^{\circ}$ to the horizontal. The block is held by a spring that is stretched $5.0 \mathrm{cm} .$ What is the force constant of the spring?

Vishal Gupta
Vishal Gupta
Numerade Educator
01:39

Problem 89

In building a house, carpenters use nails from a large box. The box is suspended from a spring twice during the day to measure the usage of nails. At the beginning of the day, the spring stretches $50 \mathrm{cm} .$ At the end of the day, the spring stretches $30 \mathrm{cm} .$ What fraction or percentage of the nails have been used?

Surjit Tewari
Surjit Tewari
Numerade Educator
01:25

Problem 90

A force is applied to a block to move it up a $30^{\circ}$ incline. The incline is frictionless. If $F=65.0 \mathrm{N}$ and $M=5.00 \mathrm{kg},$ what is the magnitude of the acceleration of the block?

Surjit Tewari
Surjit Tewari
Numerade Educator
03:17

Problem 91

Two forces are applied to a 5.0 -kg object, and it accelerates at a rate of $2.0 \mathrm{m} / \mathrm{s}^{2}$ in the positive $y$ -direction. If one of the forces acts in the positive $x$ -direction with magnitude $12.0 \mathrm{N},$ find the magnitude of the other force.

Vishal Gupta
Vishal Gupta
Numerade Educator
00:58

Problem 92

The block on the right shown below has more mass than the block on the left $\left(m_{2}>m_{1}\right) .$ Draw free-body diagrams for each block.

Surjit Tewari
Surjit Tewari
Numerade Educator
01:13

Problem 93

If two tugboats pull on a disabled vessel, as shown here in an overhead view, the disabled vessel will be pulled along the direction indicated by the result of the exerted forces. (a) Draw a free-body diagram for the vessel. Assume no friction or drag forces affect the vessel. (b) Did you include all forces in the overhead view in your free body diagram? Why or why not?

Surjit Tewari
Surjit Tewari
Numerade Educator
03:36

Problem 94

A 10.0 -kg object is initially moving east at $15.0 \mathrm{m} /$ s. Then a force acts on it for $2.00 \mathrm{s}$, after which it moves northwest, also at $15.0 \mathrm{m} / \mathrm{s}$. What are the magnitude and direction of the average force that acted on the object over the $2.00-\mathrm{s}$ interval?

Surjit Tewari
Surjit Tewari
Numerade Educator
03:48

Problem 95

On June 25, 1983, shot-putter Udo Beyer of East Germany threw the $7.26-\mathrm{kg}$ shot $22.22 \mathrm{m}$, which at that time was a world record. (a) If the shot was released at a height of $2.20 \mathrm{m}$ with a projection angle of $45.0^{\circ},$ what was its initial velocity? (b) If while in Beyer's hand the shot was accelerated uniformly over a distance of $1.20 \mathrm{m},$ what was the net force on it?

Surjit Tewari
Surjit Tewari
Numerade Educator
01:10

Problem 96

A body of mass $m$ moves in a horizontall direction $x(t)=a t^{4}+b t^{3}+c t, \quad$ where $a, b,$ and $c$ are constants. (a) What is the acceleration of the body? (b) What is the timedependent force acting on the body?

Surjit Tewari
Surjit Tewari
Numerade Educator
05:23

Problem 97

A body of mass $m$ has initial velocity $v_{0}$ in the positive $x$ -direction. It is acted on by a constant force $F$ for time $t$ until the velocity becomes zero; the force continues to act on the body until its velocity becomes $-v_{0}$ in the
same amount of time. Write an expression for the total distance the body travels in terms of the variables indicated.

Linda Winkler
Linda Winkler
Numerade Educator
01:54

Problem 98

The velocities of a 3.0 -kg object at $t=6.0 \mathrm{s}$ and $t=8.0 \mathrm{s} \quad$ are $\quad(3.0 \hat{\mathrm{i}}-6.0 \hat{\mathrm{j}}+4.0 \hat{\mathrm{k}}) \mathrm{m} / \mathrm{s} \quad$ and
$(-2.0 \hat{\mathbf{i}}+4.0 \hat{\mathbf{k}}) \mathrm{m} / \mathrm{s},$ respectively. If the object is moving at constant acceleration, what is the force acting on it?

Surjit Tewari
Surjit Tewari
Numerade Educator
02:24

Problem 99

A 120-kg astronaut is riding in a rocket sled that is sliding along an inclined plane. The sled has a horizontal component of acceleration of $5.0 \mathrm{m} / \mathrm{s}^{2}$ and a downward component of $3.8 \mathrm{m} / \mathrm{s}^{2} .$ Calculate the magnitude of the force on the rider by the sled. (Hint: Remember that gravitational acceleration must be considered.)

Surjit Tewari
Surjit Tewari
Numerade Educator
01:22

Problem 100

Two forces are acting on a 5.0 -kg object that moves with acceleration $2.0 \mathrm{m} / \mathrm{s}^{2}$ in the positive $y$ -direction. If one of the forces acts in the positive $x$ -direction and has magnitude of $12 \mathrm{N},$ what is the magnitude of the other force?

Surjit Tewari
Surjit Tewari
Numerade Educator
02:51

Problem 101

Suppose that you are viewing a soccer game from a helicopter above the playing field. Two soccer players simultaneously kick a stationary soccer ball on the flat field; the soccer ball has mass 0.420 kg. The first player kicks with force $162 \mathrm{N}$ at $9.0^{\circ}$ north of west. At the same instant, the second player kicks with force $215 \mathrm{N}$ at $15^{\circ}$ east of south. Find the acceleration of the ball in $\hat{\mathbf{i}}$ and $\hat{\mathbf{j}}$
form.

Surjit Tewari
Surjit Tewari
Numerade Educator
01:01

Problem 102

A 10.0 -kg mass hangs from a spring that has the spring constant $535 \mathrm{N} / \mathrm{m}$. Find the position of the end of the spring away from its rest position. (Use $g=9.80 \mathrm{m} / \mathrm{s}^{2}$.)

Surjit Tewari
Surjit Tewari
Numerade Educator
01:53

Problem 103

A 0.0502-kg pair of fuzzy dice is attached to the rearview mirror of a car by a short string. The car accelerates at constant rate, and the dice hang at an angle of $3.20^{\circ}$ from the vertical because of the car's acceleration. What is the magnitude of the acceleration of the car?

Surjit Tewari
Surjit Tewari
Numerade Educator
02:48

Problem 104

At a circus, a donkey pulls on a sled carrying a small clown with a force given by $2.48 \hat{\mathbf{i}}+4.33 \hat{\mathbf{j}} \mathrm{N}$. A horse pulls on the same sled, aiding the hapless donkey, with a force of $6.56 \hat{\mathbf{i}}+5.33 \hat{\mathbf{j}} \mathrm{N} .$ The mass of the sled is 575
kg. Using í and $\hat{\mathbf{j}}$ form for the answer to each problem, find (a) the net force on the sled when the two animals act together, (b) the acceleration of the sled, and (c) the velocity after $6.50 \mathrm{s}.$

Surjit Tewari
Surjit Tewari
Numerade Educator
08:53

Problem 105

Hanging from the ceiling over a baby bed, well out of baby's reach, is a string with plastic shapes, as shown here. The string is taut (there is no slack), as shown by the straight segments. Each plastic shape has the same mass $m,$ and they are equally spaced by a distance $d,$ as shown. The angles labeled $\theta$ describe the angle formed by the end of the string and the ceiling at each end. The center length of sting is horizontal. The remaining two segments each form an angle with the horizontal, labeled $\phi .$ Let $T_{1}$ be the tension in the leftmost section of the string, $T_{2}$ be the tension in the section adjacent to it, and $T_{3}$ be the tension in the horizontal segment. (a) Find an equation for the tension in each section of the string in terms of the variables $m, g,$ and $\theta .$ (b) Find the angle $\phi$ in terms of the angle $\theta$. (c) If $\theta=5.10^{\circ},$ what is the value of $\phi$ ? (d) Find the distance $x$ between the endpoints in terms of $d$ and $\theta$.

Surjit Tewari
Surjit Tewari
Numerade Educator
01:37

Problem 106

A bullet shot from a rifle has mass of $10.0 \mathrm{g}$ and travels to the right at $350 \mathrm{m} / \mathrm{s}$. It strikes a target, a large bag of sand, penetrating it a distance of $34.0 \mathrm{cm} .$ Find the magnitude and direction of the retarding force that slows and stops the bullet.

Surjit Tewari
Surjit Tewari
Numerade Educator
03:45

Problem 107

An object is acted on by three simultaneous forces:
$\overrightarrow{\mathbf{F}}_{1}=(-3.00 \hat{\mathbf{i}}+2.00 \hat{\mathbf{j}}) \mathrm{N}$
$\overrightarrow{\mathbf{F}}_{2}=(6.00 \hat{\mathbf{i}}-4.00 \hat{\mathbf{j}}) \mathrm{N}, \quad$ and
$\overrightarrow{\mathbf{F}}_{3}=(2.00 \hat{\mathbf{i}}+5.00 \hat{\mathbf{j}}) \mathrm{N} .$ The object experiences acceleration of $4.23 \mathrm{m} / \mathrm{s}^{2} .$ (a) Find the acceleration vector in terms of $m$. (b) Find the mass of the object. (c) If the object begins from rest, find its speed after 5.00 s. (d) Find the components of the velocity of the object after 5.00 S.

Surjit Tewari
Surjit Tewari
Numerade Educator
01:36

Problem 108

In a particle accelerator, a proton has mass to a nar a paton has mass $1.67 \times 10^{-27} \mathrm{kg}$ and an initial speed of $2.00 \times 10^{5} \mathrm{m} / \mathrm{s}$ It moves in a straight line, and its speed increases to $9.00 \times 10^{5} \mathrm{m} / \mathrm{s}$ in a distance of $10.0 \mathrm{cm} .$ Assume that the acceleration is constant. Find the magnitude of the force exerted on the proton.

Surjit Tewari
Surjit Tewari
Numerade Educator
04:07

Problem 109

A drone is being directed across a frictionless icecovered lake. The mass of the drone is $1.50 \mathrm{kg}$, and its velocity is $3.00 \hat{\mathbf{i}} \mathrm{m} / \mathrm{s}$. After $10.0 \mathrm{s}$, the velocity is
$9.00 \hat{\mathbf{i}}+4.00 \hat{\mathbf{j}} \mathrm{m} / \mathrm{s} .$ If a constant force in the horizontal direction is causing this change in motion, find (a) the components of the force and (b) the magnitude of the force.

Rodger Claar
Rodger Claar
Numerade Educator