• Home
  • Textbooks
  • College Physics: A Strategic Approach
  • Momentum

College Physics: A Strategic Approach

Randall D. Knight, Brian Jones, Stuart Field

Chapter 9

Momentum - all with Video Answers

Educators

+ 1 more educators

Chapter Questions

01:22

Problem 1

At what speed do a bicycle and its rider, with a combined mass of $100 \mathrm{kg},$ have the same momentum as a $1500 \mathrm{kg}$ car traveling at $1.0 \mathrm{m} / \mathrm{s}$ ?

Aditya Sood
Aditya Sood
Numerade Educator
01:42

Problem 2

Two physics students are doing a side competition during a game of bowling, seeing who can toss a ball with the larger momentum. The first bowler throws a $4.5 \mathrm{kg}$ ball at $7.2 \mathrm{m} / \mathrm{s}$. A second bowler throws a $6.4 \mathrm{kg}$ ball. What speed must she beat to win the competition?

Aditya Sood
Aditya Sood
Numerade Educator
01:48

Problem 3

A 57 g tennis ball is served at $45 \mathrm{m} / \mathrm{s}$. If the ball started from rest, what impulse was applied to the ball by the racket?

Aditya Sood
Aditya Sood
Numerade Educator
03:24

Problem 4

A large raindrop - the type that lands with a definite splathas a mass of 0.014 g and hits your roof at a speed of $8.1 \mathrm{m} / \mathrm{s}$.
a. What is the magnitude of the impulse delivered to your roof?
b. If the raindrop comes to rest in $0.37 \mathrm{ms},$ what is the magnitude of the average force of the impact?

Aditya Sood
Aditya Sood
Numerade Educator
02:35

Problem 5

A student throws a 120 g snowball at $7.5 \mathrm{m} / \mathrm{s}$ at the side of the schoolhouse, where it hits and sticks. What is the magnitude of the average force on the wall if the duration of the collision is $0.15 \mathrm{s} ?$

Aditya Sood
Aditya Sood
Numerade Educator
01:55

Problem 6

Model rocket engines are rated by the impulse that they deliver when they fire. A particular engine is rated to deliver an impulse of $3.5 \mathrm{kg} \cdot \mathrm{m} / \mathrm{s} .$ The engine powers a $120 \mathrm{g}$ rocket, including the mass of the engine. What is the final speed of the rocket once the engine has fired? (Ignore the change in mass as the engine fires and ignore the weight force during the short duration firing of the engine.)

Aditya Sood
Aditya Sood
Numerade Educator
01:51

Problem 7

III In Figure P9.7, what value of $F_{\max }$ gives an impulse of $6.0 \mathrm{N} \cdot \mathrm{s} ?$
FIGURE P9.7

Aditya Sood
Aditya Sood
Numerade Educator
05:02

Problem 8

A billiard ball of mass $0.28 \mathrm{kg}$ hits a second, identical ball at a speed of $7.2 \mathrm{m} / \mathrm{s}$ and comes to rest as the second ball flies off. The collision takes $250 \mu$ s. What is the average force on the first ball? The second ball?

Aditya Sood
Aditya Sood
Numerade Educator
02:37

Problem 9

Use the impulse-momentum theorem to find how long a stone falling straight down takes to increase its speed from $5.5 \mathrm{m} / \mathrm{s}$ to $10.4 \mathrm{m} / \mathrm{s}$

Aditya Sood
Aditya Sood
Numerade Educator
02:55

Problem 10

I trap-jaw ant snaps its mandibles shut at very high speed, a good trait for catching small prey. But an ant can also slam its mandibles into the ground; the resulting force can launch the ant into the air for a quick escape. A 12 mg ant hits the ground with an average force of $47 \mathrm{mN}$ for a time of $0.13 \mathrm{ms} ;$ these are all typical values. At what speed does it leave the ground?

Guilherme Barros
Guilherme Barros
Numerade Educator
03:15

Problem 11

A 60 g tennis ball with an initial speed of $32 \mathrm{m} / \mathrm{s}$ hits a wall and rebounds with the same speed. Figure $\mathrm{P} 9.11$ shows the force of the wall
on the ball during the collision. What is the value of $F_{\max },$ the maximum value of the contact force during the collision?

Aditya Sood
Aditya Sood
Numerade Educator
02:24

Problem 12

Investigators studying the effect of hitting a soccer ball with the head are using a force plate to look at the forces in ball collisions; the force when the ball hits a player's head will be similar. A $0.43 \mathrm{kg}$ ball is launched at a force plate at $16 \mathrm{m} / \mathrm{s}$. Smoothed data for the force versus time for the collision are shown in Figure $\mathrm{P} 9.12 .$ At what speed does the ball rebound from the plate?

Susan Hallstrom
Susan Hallstrom
Numerade Educator
02:50

Problem 13

A child is sliding on a sled at $1.5 \mathrm{m} / \mathrm{s}$ to the right. You stop the sled by pushing on it for 0.50 s in a direction opposite to its motion. If the mass of the child and sled is $35 \mathrm{kg}$, what average force do you need to apply to stop the sled? Use the concepts of impulse and momentum.

Aditya Sood
Aditya Sood
Numerade Educator
03:13

Problem 14

Ferns spread spores instead of seeds, and some ferns eject the spores at surprisingly high speeds. One species accelerates $1.4 \mu \mathrm{g}$ spores to a $4.5 \mathrm{m} / \mathrm{s}$ ejection speed in a time of $1.0 \mathrm{ms}$ What impulse is provided to the spores? What is the average force on a spore?

Guilherme Barros
Guilherme Barros
Numerade Educator
02:44

Problem 15

I As part of a safety investigation, two $1400 \mathrm{kg}$ cars traveling at $20 \mathrm{m} / \mathrm{s}$ are crashed into different barriers. Find the average forces exerted on (a) the car that hits a line of water barrels and takes $1.5 \mathrm{s}$ to stop, and (b) the car that hits a concrete barrier and takes $0.10 \mathrm{s}$ to stop.

Sachin Rao
Sachin Rao
Numerade Educator
04:59

Problem 16

Climbing ropes stretch when they catch a falling climber, thus increasing the time it takes the climber to come to rest and reducing the force on the climber. In one standardized test of ropes, an $80 \mathrm{kg}$ mass falls $4.8 \mathrm{m}$ before being caught by a $2.5-\mathrm{m}$ -long rope. If the net force on the mass must be kept below $11 \mathrm{kN},$ what is the minimum time for the mass to come to rest at the end of the fall?

Guilherme Barros
Guilherme Barros
Numerade Educator
03:53

Problem 17

In a Little League baseball game, the 145 g ball reaches the batter with a speed of $15.0 \mathrm{m} / \mathrm{s}$. The batter hits the ball, and it leaves his bat with a speed of $20.0 \mathrm{m} / \mathrm{s}$ in exactly the opposite direction.
What is the magnitude of the impulse delivered by the bat to the ball?
b. If the bat is in contact with the ball for $1.5 \mathrm{ms},$ what is the magnitude of the average force exerted by the bat on the ball?

Aditya Sood
Aditya Sood
Numerade Educator
04:36

Problem 18

The flowers of the bunchberry plant open with astonishing force and speed, with pollen grains accelerating from rest to $7.5 \mathrm{m} / \mathrm{s}$.
a.What impulse is delivered to a $1.0 \times 10^{-10} \mathrm{kg}$ pollen grain?
b. What is the average force if this impulse is delivered in $0.30 \mathrm{ms} ?$
c. How does this force compare to the weight of the pollen grain?

Guilherme Barros
Guilherme Barros
Numerade Educator
01:10

Problem 19

A small, 100 g cart is moving at $1.20 \mathrm{m} / \mathrm{s}$ on a frictionless track when it collides with a larger, $1.00 \mathrm{kg}$ cart at rest. After the collision, the small cart recoils at $0.850 \mathrm{m} / \mathrm{s}$. What is the speed of the large cart after the collision?

Aditya Sood
Aditya Sood
Numerade Educator
01:50

Problem 20

In principle, when you fire a rifle, the recoil should push you backward. How big a push will it give? Let's find out by doing a calculation in a very artificial situation. Suppose a man standing on frictionless ice fires a rifle horizontally. The mass of the man together with the rifle is $70 \mathrm{kg},$ and the mass of the bullet is 10 g. If the bullet leaves the muzzle at a speed of $500 \mathrm{m} / \mathrm{s},$ what is the final speed of the man? Given your result, do you expect to be pushed backward when you fire a rifle?

Aditya Sood
Aditya Sood
Numerade Educator
02:52

Problem 21

III $\mathrm{A} 2.7 \mathrm{kg}$ block of wood sits on a frictionless table. $\mathrm{A} 3.0 \mathrm{g}$ bullet, fired horizontally at a speed of $500 \mathrm{m} / \mathrm{s},$ goes completely through the block, emerging at a speed of $220 \mathrm{m} / \mathrm{s}$. What is the speed of the block immediately after the bullet exits?

Aditya Sood
Aditya Sood
Numerade Educator
01:46

Problem 22

Squid rely on jet propulsion when a rapid escape is necessary. A $1.5 \mathrm{kg}$ squid at rest pulls $0.10 \mathrm{kg}$ of water into its mantle, then ejects this water at a remarkable $45 \mathrm{m} / \mathrm{s} .$ Right after this ejection, how fast is the squid moving?

Aditya Sood
Aditya Sood
Numerade Educator
01:49

Problem 23

A 10,000 kg railroad car is rolling at $2.00 \mathrm{m} / \mathrm{s}$ when $\mathrm{a} 4000 \mathrm{kg}$ load of gravel is suddenly dropped in. What is the car's speed just after the gravel is loaded?

Aditya Sood
Aditya Sood
Numerade Educator
02:53

Problem 24

Some species of jellyfish use jet propulsion to get around, a much gentler form of jet propulsion than squid use. A small jellyfish takes water into its bell; the total mass of jellyfish and water is $3.2 \mathrm{g}$. The jellyfish then rapidly ejects $1.3 \mathrm{g}$ of water, achieving a speed of $0.070 \mathrm{m} / \mathrm{s}$. What is the speed of the ejected water?

Aditya Sood
Aditya Sood
Numerade Educator
02:45

Problem 25

A 55 kg hunter, standing on frictionless ice, shoots a 42 g bullet at a speed of $620 \mathrm{m} / \mathrm{s}$. What is the recoil speed of the hunter?

Aditya Sood
Aditya Sood
Numerade Educator
02:23

Problem 26

If you free the cork in a highly pressurized champagne bottle, the resulting launch of the cork will, in principle, cause the bottle to recoil. A filled champagne bottle has a mass of $1.8 \mathrm{kg}$. The cork has a mass of $7.5 \mathrm{g}$ and is launched at $20 \mathrm{m} / \mathrm{s}$. If the bottle could move freely, with what speed would it recoil? Is this something you are likely to notice?

Aditya Sood
Aditya Sood
Numerade Educator
03:32

Problem 27

$\mathrm{A} 300 \mathrm{g}$ bird flying along at $6.0 \mathrm{m} / \mathrm{s}$ sees a $10 \mathrm{g}$ insect heading straight toward it with a speed of $30 \mathrm{m} / \mathrm{s}$. The bird opens its mouth wide and enjoys a nice lunch. What is the bird's speed immediately after swallowing?

Aditya Sood
Aditya Sood
Numerade Educator
04:41

Problem 28

Peregrine falcons frequently grab prey birds from the air, as in Example 9.10. Sometimes they strike at high enough speeds that the force of the impact disables prey birds. A 480 g peregrine falcon high in the sky spies a 240 g pigeon some distance below. The falcon slows to a near stop, then goes into a dive $-$ called a stoop - and picks up speed as she falls. The falcon reaches a vertical speed of $45 \mathrm{m} / \mathrm{s}$ before striking the pigeon, which we can assume is stationary. The falcon strikes the pigeon and grabs it in her talons. The collision between the birds lasts 0.015 s.
a. What is the final speed of the falcon and pigeon?
b. What is the average force on the pigeon during the impact?

Guilherme Barros
Guilherme Barros
Numerade Educator
02:38

Problem 29

$\mathrm{A} 71 \mathrm{kg}$ baseball player jumps straight up to catch a hard-hit ball. If the 140 g ball is moving horizontally at $28 \mathrm{m} / \mathrm{s}$, and the catch is made when the ballplayer is at the highest point of his leap, what is his speed immediately after stopping the ball?

Aditya Sood
Aditya Sood
Numerade Educator
02:39

Problem 30

In a football game, a 90 kg receiver leaps straight up in the air to catch the $0.42 \mathrm{kg}$ ball the quarterback threw to him at a vigorous $21 \mathrm{m} / \mathrm{s},$ catching the ball at the highest point in his jump. Right after catching the ball, how fast is the receiver moving? Is he likely to notice this recoil?

Aditya Sood
Aditya Sood
Numerade Educator
04:17

Problem 31

A kid at the junior high cafeteria wants to propel an empty milk carton along a lunch table by hitting it with a $3.0 \mathrm{g}$ spit ball. If he wants the speed of the 20 g carton just after the spit ball hits it to be $0.30 \mathrm{m} / \mathrm{s},$ at what speed should his spit ball hit the carton?

Guilherme Barros
Guilherme Barros
Numerade Educator
04:59

Problem 32

The parking brake on a $2000 \mathrm{kg}$ Cadillac has failed, and it is rolling slowly, at $1 \mathrm{mph},$ toward a group of small children. Seeing the situation, you realize you have just enough time to drive your 1000 kg Volkswagen head-on into the Cadillac and save the children. With what speed should you impact the Cadillac to bring it to a halt?

Guilherme Barros
Guilherme Barros
Numerade Educator
02:31

Problem 33

A $2.0 \mathrm{kg}$ block slides along a frictionless surface at $1.0 \mathrm{m} / \mathrm{s}$. A second block, sliding at $4.0 \mathrm{m} / \mathrm{s},$ collides with the first from behind and sticks to it. The final velocity of the combined blocks is $2.0 \mathrm{m} / \mathrm{s}$. What was the mass of the second block?

Aditya Sood
Aditya Sood
Numerade Educator
05:05

Problem 34

Erica $(36 \mathrm{kg})$ and Danny $(47 \mathrm{kg})$ are bouncing on a trampoline. Just as Erica reaches the high point of her bounce, Danny is moving upward past her at $4.1 \mathrm{m} / \mathrm{s}$. At that instant he grabs hold of her. What is their speed just after he grabs her?

Guilherme Barros
Guilherme Barros
Numerade Educator
05:23

Problem 35

A 20 g ball of clay traveling east at $3.0 \mathrm{m} / \mathrm{s}$ collides with a 30 g ball of clay traveling north at $2.0 \mathrm{m} / \mathrm{s}$. What are the speed and the direction of the resulting 50 g blob of clay?

Guilherme Barros
Guilherme Barros
Numerade Educator
08:17

Problem 36

Casey is driving a $1600 \mathrm{kg}$ car toward the east. She goes through an intersection at a speed of $16 \mathrm{m} / \mathrm{s}$ (approximately $35 \mathrm{mph}),$ the speed limit on both roads of the intersection. Kerry is driving a car of mass $1200 \mathrm{kg}$ into the intersection, going north, and doesn't see or doesn't heed a red light, and slams into Casey's car. The cars lock together and skid to a stop. Later, the two review the scene with the police. Skid marks from the instant after the collision reveal that the two cars were moving exactly northeast. Kerry claims to have been driving at the speed limit, but Casey says that Kerry seemed to be going over the speed limit before the collision. Who is correct? Use the concept of conservation of momentum to make your case.

Guilherme Barros
Guilherme Barros
Numerade Educator
03:46

Problem 37

II Two objects collide and bounce apart. Figure P9.37 shows the initial momentum of each object and the final momentum of object $2 .$ What is the final momentum of object 1? Show your answer by copying the figure and drawing the final momentum vector on the figure.

Guilherme Barros
Guilherme Barros
Numerade Educator
09:40

Problem 38

A $20 \mathrm{g}$ ball of clay traveling east at $2.0 \mathrm{m} / \mathrm{s}$ collides with a $30 \mathrm{g}$ ball of clay traveling $30^{\circ}$ south of west at $1.0 \mathrm{m} / \mathrm{s}$. What are the speed and direction of the resulting $50 \mathrm{g}$ blob of clay?

Dading Chen
Dading Chen
Numerade Educator
03:40

Problem 39

A firecracker in a coconut blows the coconut into three
pieces. Two pieces of equal mass fly off south and west, perpendicular to each other, at $20 \mathrm{m} / \mathrm{s}$. The third piece has twice the mass of the other two. What are the speed and direction of the third piece?

Aditya Sood
Aditya Sood
Numerade Educator
02:28

Problem 40

What is the angular momentum about the axle of the $500 \mathrm{g}$ rotating bar in Figure $\mathrm{P} 9.40 ?$

Aditya Sood
Aditya Sood
Numerade Educator
02:45

Problem 41

What is the angular momentum about the axle of the $2.0 \mathrm{kg}$, 4.0-cm-diameter rotating disk in Figure P9.41?

Aditya Sood
Aditya Sood
Numerade Educator
01:19

Problem 42

Divers change their body position in midair while rotating about their center of mass. In one dive, the diver leaves the board with her body nearly straight, then tucks into a somersault position. If the moment of inertia of the diver in a straight position is $14 \mathrm{kg} \cdot \mathrm{m}^{2}$ and in a tucked position is $4.0 \mathrm{kg} \cdot \mathrm{m}^{2},$ by what factor does her angular speed increase?

Aditya Sood
Aditya Sood
Numerade Educator
01:51

Problem 43

$\|$ Ice skaters often end their performances with spin turns, where they spin very fast about their center of mass with their arms folded in and legs together. Upon ending, their arms extend outward, proclaiming their finish. Not quite as noticeably, one leg goes out as well. Suppose that the moment of inertia of a skater with arms out and one leg extended is $3.2 \mathrm{kg} \cdot \mathrm{m}^{2}$ and for arms and legs in is $0.80 \mathrm{kg} \cdot \mathrm{m}^{2}$. If she starts out spinning at 5.0 rev/s, what is her angular speed (in rev/s) when her arms and one leg open outward?

Aditya Sood
Aditya Sood
Numerade Educator
06:43

Problem 44

Ill A diver leaves the platform with her body straight. Her body is in a relatively slow rotation, with an angular speed of $4.0 \mathrm{rad} / \mathrm{s}$. She then tucks into a pike position, with her body essentially folded in half. We can use a simple model to understand what happens next. First, model her $50 \mathrm{kg}, 1.8 \mathrm{m}$ body as uniform. Next, assume that when she goes into a pike position, she really does fold her body exactly in half. In terms of this model,
a. What is her initial moment of inertia?
b. What is her moment of inertia in the pike position?
c. What is her angular speed in the pike position?
d. How many rotations does she complete in the $1.3 \mathrm{s}$ that she holds the pike position?

Vishal Gupta
Vishal Gupta
Numerade Educator
03:33

Problem 45

What is the angular momentum of the moon around $\mathbb{N}$ the earth? The moon's mass is $7.4 \times 10^{22} \mathrm{kg}$ and it orbits $3.8 \times 10^{8} \mathrm{m}$ from the earth.

Aditya Sood
Aditya Sood
Numerade Educator
01:31

Problem 46

III What is the impulse on a $3.0 \mathrm{kg}$ object that experiences the force described by the graph in Figure $\mathrm{P} 9.46 ?$

Aditya Sood
Aditya Sood
Numerade Educator
03:46

Problem 47

A 600 g air-track glider collides with a spring at one end of the track. Figure P9.47 shows the glider's velocity and the force exerted on the glider by the spring. How long is the glider in contact with the spring?

Guilherme Barros
Guilherme Barros
Numerade Educator
04:52

Problem 48

I Far in space, where gravity is negligible, a $425 \mathrm{kg}$ rocket traveling at $75.0 \mathrm{m} / \mathrm{s}$ in the positive $x$ -direction fires its engines. Figure $\mathrm{P} 9.48$ shows the thrust force as a function of time. The
mass lost by the rocket during these $30.0 \mathrm{s}$ is negligible.
a. What impulse does the engine impart to the rocket?
b. At what time does the rocket reach its maximum speed? What is the maximum speed?

Guilherme Barros
Guilherme Barros
Numerade Educator
05:28

Problem 49

$\begin{array}{lllll}\text { Illl } \mathrm{A} & 200 & \mathrm{g} & \text { ball } & \text { is }\end{array}$
dropped from a height of $2.0 \mathrm{m},$ bounces on a hard floor, and rebounds to a height of $1.5 \mathrm{m} .$ Figure P9.49 shows the impulse received from the floor.
What maximum force
does the floor exert on
the ball?

Aditya Sood
Aditya Sood
Numerade Educator
04:37

Problem 50

A 200 g ball is dropped from a height of $2.0 \mathrm{m}$ and bounces on a hard floor.
The force on the ball from
the floor is shown in Figure P9.50. How high does the ball rebound?

Aditya Sood
Aditya Sood
Numerade Educator
06:35

Problem 51

Figure $\mathrm{P} 9.51$ is a graph of the force exerted by the floor on a woman making a vertical jump. At what speed does she leave the ground? Hint: The force of the floor
is not the only force acting on the woman.

Susan Hallstrom
Susan Hallstrom
Numerade Educator
04:31

Problem 52

We've seen that squid can escape from predators by ejecting water. Some squid do this at the surface of the ocean, thus launching themselves into the air-a particularly effective escape strategy. Suppose a $36 \mathrm{kg}$ squid (not including water) at rest at the surface of the water brings in and quickly ejects $3.0 \mathrm{kg}$ of water to achieve a takeoff speed of $3.5 \mathrm{m} / \mathrm{s} ;$ these are typical numbers.
a. At what speed does the squid eject the water?
b. If we ignore lift and drag forces as the squid flies through the air, what is the maximum horizontal range that the squid can achieve before splashing down?

Guilherme Barros
Guilherme Barros
Numerade Educator
07:54

Problem 53

$\mathrm{A} 140 \mathrm{g}$ baseball is moving horizontally to the right at $35 \mathrm{m} / \mathrm{s}$ when it is hit by the bat. The ball flies off to the left at $55 \mathrm{m} / \mathrm{s},$ at an angle of $25^{\circ}$ above the horizontal. What are the magnitude and direction of the impulse that the bat delivers to the ball?

Guilherme Barros
Guilherme Barros
Numerade Educator
05:53

Problem 54

A tennis player swings her 1000 g racket with a speed of $10 \mathrm{m} / \mathrm{s} .$ She hits a $60 \mathrm{g}$ tennis ball that was approaching her at a speed of $20 \mathrm{m} / \mathrm{s} .$ The ball rebounds at $40 \mathrm{m} / \mathrm{s} .$
a. How fast is her racket moving immediately after the impact? You can ignore the interaction of the racket with her hand for the brief duration of the collision.
b. If the tennis ball and racket are in contact for $10 \mathrm{ms}$, what is the average force that the racket exerts on the ball?

Guilherme Barros
Guilherme Barros
Numerade Educator
06:04

Problem 55

II A 20 g ball of clay is thrown horizontally at $30 \mathrm{m} / \mathrm{s}$ toward
a $1.0 \mathrm{kg}$ block sitting at rest on a frictionless surface. The clay hits and sticks to the block.
a. What is the speed of the block and clay right after the collision?
b. Use the block's initial and final speeds to calculate the impulse the clay exerts on the block.
c. Use the clay's initial and final speeds to calculate the impulse the block exerts on the clay.
d. Does $\vec{J}_{\text {blockonclay }}=-\vec{J}_{\text {clayon block }} ?$

Guilherme Barros
Guilherme Barros
Numerade Educator
02:44

Problem 56

Dan is gliding on his skateboard at $4.0 \mathrm{m} / \mathrm{s} .$ He jumps backward off the skateboard, kicking the skateboard forward at $8.0 \mathrm{m} / \mathrm{s} .$ How fast is Dan going as his feet hit the ground? Dan's mass is $50 \mathrm{kg}$ and the skateboard's mass is $5.0 \mathrm{kg}$.

Aditya Sood
Aditya Sood
Numerade Educator
02:50

Problem 57

Ethan, whose mass is $80 \mathrm{kg}$, stands at one end of a very long, stationary wheeled cart that has a mass of $500 \mathrm{kg} .$ He then starts sprinting toward the other end of the cart. He soon reaches his top speed of $8.0 \mathrm{m} / \mathrm{s}$, measured relative to the cart. What is the cart's speed when Ethan reaches top speed?

Aditya Sood
Aditya Sood
Numerade Educator
01:40

Problem 58

II Three identical train cars, coupled together, are rolling east at $2.0 \mathrm{m} / \mathrm{s} .$ A fourth car traveling east at $4.0 \mathrm{m} / \mathrm{s}$ catches up with the three and couples to make a four-car train. A moment later, the train cars hit a fifth car that was at rest on the tracks, and it couples to make a five-car train. What is the speed of the fivecar train?

Aditya Sood
Aditya Sood
Numerade Educator
03:01

Problem 59

A 110 kg linebacker running at $2.0 \mathrm{m} / \mathrm{s}$ and an $82 \mathrm{kg}$ quarterback running at $3.0 \mathrm{m} / \mathrm{s}$ have a head-on collision in midair. The linebacker grabs and holds onto the quarterback. Who ends up moving forward after they hit?

Aditya Sood
Aditya Sood
Numerade Educator
04:16

Problem 60

II Most geologists believe that the dinosaurs became extinct
65 million years ago when a large comet or asteroid struck the earth, throwing up so much dust that the sun was blocked out for a period of many months. Suppose an asteroid with a diameter of $2.0 \mathrm{km}$ and a mass of $1.0 \times 10^{13} \mathrm{kg}$ hits the earth with an impact speed of $4.0 \times 10^{4} \mathrm{m} / \mathrm{s}$
a. What is the earth's recoil speed after such a collision? (Use a reference frame in which the earth was initially at rest.)
b. What percentage is this of the earth's speed around the sun? (Use the astronomical data inside the back cover.)

Guilherme Barros
Guilherme Barros
Numerade Educator
05:12

Problem 61

Two ice skaters, with masses of $75 \mathrm{kg}$ and $55 \mathrm{kg},$ stand facing each other on a $15-\mathrm{m}$ -wide frozen river. The skaters push off against each other, glide backward straight toward the river's edges, and reach the edges at exactly the same time. How far did the 75 kg skater glide?

Guilherme Barros
Guilherme Barros
Numerade Educator
03:00

Problem 62

Two ice skaters, with masses of $50 \mathrm{kg}$ and $75 \mathrm{kg}$, are at the center of a $60-\mathrm{m}$ -diameter circular rink. The skaters push off against each other and glide to opposite edges of the rink. If the heavier skater reaches the edge in 20 s, how long does the lighter skater take to reach the edge?

Dading Chen
Dading Chen
Numerade Educator
06:57

Problem 63

One billiard ball is shot east at $2.00 \mathrm{m} / \mathrm{s}$. A second, identical
billiard ball is shot west at $1.00 \mathrm{m} / \mathrm{s}$. The balls have a glancing collision, not a head-on collision, deflecting the second ball by $90^{\circ}$ and sending it north at $1.41 \mathrm{m} / \mathrm{s}$. What are the speed and direction of the first ball after the collision?

Guilherme Barros
Guilherme Barros
Numerade Educator
05:30

Problem 64

$\mathrm{A}$ 10 g bullet is fired into a $10 \mathrm{kg}$ wood block that is at rest on a wood table. The block, with the bullet embedded, slides $5.0 \mathrm{cm}$ across the table. What was the speed of the bullet?

Aditya Sood
Aditya Sood
Numerade Educator
04:02

Problem 65

$A$ typical raindrop is much more massive than a mosquito and much faster than a mosquito flies. How does a mosquito survive the impact? Recent research has found that the collision of a falling raindrop with a mosquito is a perfectly inelastic collision. That is, the mosquito is "swept up" by the raindrop and ends up traveling along with the raindrop. Once the relative speed between the mosquito and the raindrop is zero, the mosquito is able to detach itself from the drop and fly away.
a. A hovering mosquito is hit by a raindrop that is 40 times as massive and falling at $8.2 \mathrm{m} / \mathrm{s},$ a typical raindrop speed. How fast is the raindrop, with the attached mosquito, falling immediately afterward if the collision is perfectly inelastic?
b. Because a raindrop is "soft" and deformable, the collision duration is a relatively long $8.0 \mathrm{ms}$. What is the mosquito's average acceleration, in $g$ 's, during the collision? The peak acceleration is roughly twice the value you found, but the mosquito's rigid exoskeleton allows it to survive accelerations of this magnitude. In contrast, humans cannot survive an acceleration of more than about $10 \mathrm{g}$.

Guilherme Barros
Guilherme Barros
Numerade Educator
04:55

Problem 66

A 15 g bullet is fired at $610 \mathrm{m} / \mathrm{s}$ into a $4.0 \mathrm{kg}$ block that sits at the edge of a $75-\mathrm{cm}$ -high table. The bullet embeds itself in the block and carries it off the table. How far from the point directly below the table's edge does the block land?

Guilherme Barros
Guilherme Barros
Numerade Educator
06:11

Problem 67

A $1500 \mathrm{kg}$ weather rocket accelerates upward at $10.0 \mathrm{m} / \mathrm{s}^{2}$. It explodes $2.00 \mathrm{s}$ after liftoff and breaks into two fragments, one twice as massive as the other. Photos reveal that the lighter fragment traveled straight up and reached a maximum height of $530 \mathrm{m} .$ What were the speed and direction of the heavier fragment just after the explosion?

Dading Chen
Dading Chen
Numerade Educator
05:37

Problem 68

A canoe is designed to have very little drag when it moves along its length. Riley, mass $52 \mathrm{kg},$ sits in a $21 \mathrm{kg}$ canoe in the middle of a lake. She dives into the water off the front of
the canoe, along the axis of the canoe. She dives forward at $1.6 \mathrm{m} / \mathrm{s}$ relative to the boat. Just after her leap,
a. How fast is she moving relative to the water?
b. How fast is the canoe moving relative to the water?

Guilherme Barros
Guilherme Barros
Numerade Educator
03:25

Problem 69

Two 500 g blocks of wood are $2.0 \mathrm{m}$ apart on a frictionless table. A 10 g bullet is fired at $400 \mathrm{m} / \mathrm{s}$ toward the blocks. It passes all the way through the first block, then embeds itself in the second block. The speed of the first block immediately afterward is $6.0 \mathrm{m} / \mathrm{s}$. What is the speed of the second block after the bullet stops?

Prabhat Tyagi
Prabhat Tyagi
Numerade Educator
06:04

Problem 70

A water pipe in a building delivers 1000 liters (with mass $1000 \mathrm{kg}$ ) of water per second. The water is moving through the pipe at $1.4 \mathrm{m} / \mathrm{s}$. The pipe has a $90^{\circ}$ bend, and the pipe will require a supporting structure, called a thrust block, at the bend, as in Figure $\mathrm{P} 9.70$. We can use the ideas of momentum and impulse to understand why. Each second, $1000 \mathrm{kg}$ of water moving at $v_{x}=1.4 \mathrm{m} / \mathrm{s}$ changes direction to move at $v_{y}=1.4 \mathrm{m} / \mathrm{s}$
a. What are the magnitude and direction of the change in momentum of the $1000 \mathrm{kg}$ of water?
b. What are the magnitude and direction of the necessary impulse?
c. This impulse takes place over 1.0 s. What is the necessary force?

Guilherme Barros
Guilherme Barros
Numerade Educator
05:48

Problem 71

$\|$ A spaceship of mass $2.0 \times 10^{6} \mathrm{kg}$ is cruising at a speed of $5.0 \times 10^{6} \mathrm{m} / \mathrm{s}$ when the antimatter reactor fails, blow-
ing the ship into three pieces. One section, having a mass of $5.0 \times 10^{5} \mathrm{kg},$ is blown straight backward with a speed of $2.0 \times 10^{6} \mathrm{m} / \mathrm{s} .$ A second piece, with mass $8.0 \times 10^{5} \mathrm{kg},$ contin-
ues forward at $1.0 \times 10^{6} \mathrm{m} / \mathrm{s} .$ What are the direction and speed of the third piece?

Guilherme Barros
Guilherme Barros
Numerade Educator
03:54

Problem 72

$\|$ At the county fair, Chris throws a $0.15 \mathrm{kg}$ baseball at a $2.0 \mathrm{kg}$ wooden milk bottle, hoping to knock it off its stand and win a prize. The ball bounces straight back at $20 \%$ of its incoming speed, knocking the bottle straight forward. What is the bottle's speed, as a percentage of the ball's incoming speed?

Guilherme Barros
Guilherme Barros
Numerade Educator
06:30

Problem 73

Figure P9.73 shows a collision between three balls of clay. The three hit simultaneously and stick together. What are the speed and direction of the resulting blob of clay?

Guilherme Barros
Guilherme Barros
Numerade Educator
05:40

Problem 74

The carbon isotope ${ }^{14} \mathrm{C}$ is used for carbon dating of archeological artifacts. ${ }^{14} \mathrm{C}$ (mass $2.34 \times 10^{-26} \mathrm{kg}$ ) decays by the process known as beta decay in which the nucleus emits an electron (the beta particle) and a subatomic particle called a neutrino. In one such decay, the electron and the neutrino are emitted at right angles to each other. The electron (mass $9.11 \times 10^{-31} \mathrm{kg}$ ) has a speed of $5.00 \times 10^{7} \mathrm{m} / \mathrm{s}$ and the neutrino has a momentum of $8.00 \times 10^{-24} \mathrm{kg} \cdot \mathrm{m} / \mathrm{s} .$ What is the recoil speed of the nucleus?

Guilherme Barros
Guilherme Barros
Numerade Educator
03:52

Problem 75

Figure $\mathrm{P} 9.75$ shows a $100 \mathrm{g}$ puck revolving at $100 \mathrm{rpm}$ on a 20-cm-radius circle on a frictionless table. A string attached to the puck passes through a hole in the middle of the table. The end of the string below the table is then slowly pulled down until the puck is revolving in a 10 -cm-radius circle. How many revolutions per minute does the puck make at this new radius?

Guilherme Barros
Guilherme Barros
Numerade Educator
05:09

Problem 76

$\mathrm{A}$ 2.0 $\mathrm{kg}, 20$ -cm-diameter turntable rotates at $100 \mathrm{rpm}$ on frictionless bearings. Two 500 g blocks fall from above, hit the turntable simultaneously at opposite ends of a diagonal, and stick. What is the turntable's angular speed, in rpm, just after this event?

Guilherme Barros
Guilherme Barros
Numerade Educator
04:42

Problem 77

Joey, from Example 9.11 , stands at rest at the outer edge of the frictionless merry-go-round of Figure $9.27 .$ The merry-goround is also at rest. Joey then begins to run around the perimeter of the merry-go-round, finally reaching a constant speed, measured relative to the ground, of $5.0 \mathrm{m} / \mathrm{s}$. What is the final angular speed of the merry-go-round?

Guilherme Barros
Guilherme Barros
Numerade Educator
07:18

Problem 78

A 3.0 -m-diameter merry-go-round with a mass of $250 \mathrm{kg}$ is spinning at 20 rpm. John runs around the merry-go-round at $5.0 \mathrm{m} / \mathrm{s},$ in the same direction that it is turning, and jumps onto the outer edge. John's mass is 30 kg. What is the merry-goround's angular speed, in rpm, after John jumps on?

Guilherme Barros
Guilherme Barros
Numerade Educator
05:36

Problem 79

Disk A, with a mass of $2.0 \mathrm{kg}$ and a radius of $40 \mathrm{cm}$, rotates clockwise about a frictionless vertical axle at 30 rev/s. Disk B, also $2.0 \mathrm{kg}$ but with a radius of $20 \mathrm{cm},$ rotates counterclockwise about that same axle, but at a greater height than disk A, at 30 rev/s. Disk $B$ slides down the axle until it lands on top of disk A, after which they rotate together. After the collision, what is their common angular speed (in rev/s) and in which direction do they rotate?

Guilherme Barros
Guilherme Barros
Numerade Educator
02:05

Problem 80

I What is the momentum of the club + ball system right before the collision?
A. $1.8 \mathrm{kg} \cdot \mathrm{m} / \mathrm{s}$
B. $8.0 \mathrm{kg} \cdot \mathrm{m} / \mathrm{s}$
C. $3220 \mathrm{kg} \cdot \mathrm{m} / \mathrm{s}$
D. $8000 \mathrm{kg} \cdot \mathrm{m} / \mathrm{s}$

Aditya Sood
Aditya Sood
Numerade Educator
00:40

Problem 81

I Immediately after the collision, the momentum of the club $+$ ball system will be
A. Less than before the collision.
B. The same as before the collision.
C. Greater than before the collision.

Aditya Sood
Aditya Sood
Numerade Educator
01:03

Problem 82

A manufacturer makes a golf ball that compresses more than a traditional golf ball when struck by a club. How will this affect the average force during the collision?
A. The force will decrease.
B. The force will not be affected.
C. The force will increase.

Aditya Sood
Aditya Sood
Numerade Educator
02:15

Problem 83

By approximately how much does the club head slow down as a result of hitting the ball?
A. $4 \mathrm{m} / \mathrm{s}$
B. $6 \mathrm{m} / \mathrm{s}$
C. $14 \mathrm{m} / \mathrm{s}$
D. 26 m/s

Aditya Sood
Aditya Sood
Numerade Educator
00:58

Problem 84

II The sauté demi plié begins with a phase in which the net force on the dancer is negative. During this phase of the jump,
A. The normal force of the floor on her is zero.
B. The normal force of the floor on her is less than her weight but greater than zero.
C. The normal force of the floor on her is equal to her weight.
D. The normal force of the floor on her is greater than her weight.

Aditya Sood
Aditya Sood
Numerade Educator
02:34

Problem 85

At what time does the dancer reach the lowest point of her motion, when her speed is zero?
A. $0.20 \mathrm{s}$
B. $0.40 \mathrm{s}$
C. Between $0.40 \mathrm{s}$ and $0.70 \mathrm{s}$
D. After $0.70 \mathrm{s}$

Aditya Sood
Aditya Sood
Numerade Educator
01:57

Problem 86

What is the approximate net impulse on the dancer, from the moment she begins bending her knees to the instant she leaves the floor?
A. $15 \mathrm{kg} \cdot \mathrm{m} / \mathrm{s}^{2}$
B. $30 \mathrm{kg} \cdot \mathrm{m} / \mathrm{s}^{2}$
C. $60 \mathrm{kg} \cdot \mathrm{m} / \mathrm{s}^{2}$
D. $90 \mathrm{kg} \cdot \mathrm{m} / \mathrm{s}^{2}$

Aditya Sood
Aditya Sood
Numerade Educator
01:11

Problem 87

II To the nearest $\mathrm{m} / \mathrm{s},$ how fast is the dancer moving when she leaves the floor?
A. $1 \mathrm{m} / \mathrm{s}$
B. $2 \mathrm{m} / \mathrm{s}$
$\mathrm{C} .3 \mathrm{m} / \mathrm{s}$
D. $4 \mathrm{m} / \mathrm{s}$

Aditya Sood
Aditya Sood
Numerade Educator