chapter6

Question 1

A slowly moving ship can have a greater momentum than a fast-moving racing car when _______.

• its mass is greater than the mass of the car
• it drifts toward a distant port.
• its speed is greater than the speed of the car.
• its mass times velocity is greater than that of the car.

Answer 1

its mass times velocity is greater than that of the car.

Question 2

A slowly moving ship can have a greater momentum than a fast-moving racing car when _______.

Answer 2

its mass times velocity is greater than that of the car.

Question 3

The quantity that is called impulse can be measured by the _______.

Answer 3

product of force and time.

Question 4

Distinguish between force and impulse.

Answer 4

Impulse is force times a time interval.

Question 5

An impulse can be increased by

Answer 5

increasing the force or increasing the time interval

Question 6

How is the impulse -momentum relationship related to Newton’s second law?

Answer 6

F=ma=mΔv/Δt
, so
Ft=Δ(mv)

Question 7

When a cannonball is fired from a cannon, the momentum of the recoiling cannon is momentarily _______.

Answer 7

equal and opposite to the momentum of the fired cannonball

Question 8

When a cue ball strikes an 8 ball head-on in a game of pool, the cue ball _______.

Answer 8

transfers its momentum to the 8 ball.

Question 9

When two vehicles collide, momentum is conserved _______.

Answer 9

whether the collision is elastic or inelastic.

Question 10

When a big fish swims into an oncoming smaller fish and swallows it, the momentum of the two-fish system _______.

Answer 10

remains the same

Question 11

Is it correct to say that, if no net impulse is exerted on a system, then no change in the momentum of the system will occur?

Answer 11

Yes, always

Question 12

When a falling firecracker explodes, the momenta of its pieces _______.

Answer 12

vectorally add up to equal the initial momentum of the firecracker

Question 13

In which is momentum conserved: an elastic collision or an inelastic collision?

Answer 13

Momentum is conserved in elastic and inelastic collisions.

Question 14

Railroad car A rolls at a certain speed and makes a perfectly elastic collision with car B of the same mass. After the collision, car A is observed to be at rest. How does the speed of car B compare with the initial speed of car A?

Answer 14

The speed of car B is equal to the initial speed of A.

Question 15

If the equally massive cars of the preceding question stick together after colliding inelastically, how does their speed after the collision compare with the initial speed of car A?

Answer 15

Their speed is half the initial speed of car A.

Question 16

Which has the greater momentum when moving?

Answer 16

either of these depending on speed

Question 17

Which of the following has the largest momentum relative to Earth’s surface?

Answer 17

a pickup truck speeding along a highway

Question 18

A freight train rolls along a track with considerable momentum. If it rolls at the same speed but has twice as much mass, its momentum is

Answer 18

twice.

Question 19

A same-size iron ball and wooden ball are dropped simultaneously from a tower and reach the ground at the same time. The iron ball has a greater

Answer 19

momentum

Question 20

The speed of a 4-kg ball with a momentum of 12 kg m/s is

Answer 20

3 m/s

Question 21

The mass of a ball moving at 3 m/s with a momentum of 48 kg m/s is

Answer 21

16 kg

Question 22

If several balls are thrown straight up with different initial speeds, the quantity that will have the same value along their paths is their

Answer 22

acceleration

Question 23

A motorcycle of mass 100 kilograms slowly rolls off the edge of a cliff and falls for three seconds before reaching the bottom of a gully. Its momentum upon hitting the ground is

Answer 23

3,000 kg m/s.

Question 24

It is correct to say that impulse is equal to

Answer 24

a corresponding change in momentum

Question 25

Padded dashboards in cars are safer in an accident than non-padded ones because passengers hitting the dashboard encounter

Answer 25

lengthened time of contact

Question 26

Compared with falling on a stone floor, a wine glass may not break when it falls on a carpeted floor because the

Answer 26

stopping time is longer on the carpet.

Question 27

When you jump from an elevated position you usually bend your knees upon reaching the ground, which makes the time of the contact about 10 times that of a stiff-legged landing. In this way the average force your body experiences is

Answer 27

about 1/10 as great.

Question 28

If you can't avoid being hit by a fast-moving object, you'll suffer a smaller contact force if you can extend that force over a

Answer 28

longer time

Question 29

Whether a truck comes to a stop by crashing into a haystack or a brick wall, the stopping force is

Answer 29

greater with the brick wall

Question 30

Whether a truck comes to a stop by crashing into a haystack or a brick wall, the impulse is

Answer 30

both the same

Question 31

A cannon recoils while firing a cannonball. The speed of the cannon's recoil is relatively small because the

Answer 31

cannon has much more mass than the cannonball

Question 32

A tiny gun made of a strong but very light material fires a bullet more massive than the gun itself. For such a weapon

Answer 32

the target would be safer than the shooter

Question 33

A heavy truck and a small car rolling down a hill at the same speed are forced to stop in the same amount of time. Compared with the force that stops the car, the force needed to stop the truck is

Answer 33

greater

Question 34

The average braking force of a 1000-kg car moving at 10 m/s braking to a stop in 5 s is

Answer 34

2000 N

Question 35

As Bronco Brown steps off a hovering high-flying helicopter and falls through the air, he experiences

Answer 35

- an impulse. - a decreasing acceleration. - an increasing speed

Question 36

When Freddy Frog drops vertically from a tree onto a horizontally-moving skateboard, the speed of the skateboard

Answer 36

decreases

Question 37

Freddy Frog drops vertically from a tree onto a horizontally-moving skateboard. The reason he doesn't slip off the skateboard is due to

Answer 37

friction between his feet and the board.

Question 38

You're driving down the highway and a bug spatters into your windshield. Which undergoes the greater change in momentum during the time of contact?

Answer 38

both the same

Question 39

An astronaut floating alone in outer space throws a baseball. If the ball moves away at 20 m/s, the astronaut will

Answer 39

move in the opposite direction at a lower speed

Question 40

Two billiard balls having the same mass and speed roll toward each other. What is their combined momentum after they meet?

Answer 40

zero

Question 41

An open freight car rolls friction free along a horizontal track in a pouring rain that falls vertically. As water accumulates in the car, the car's speed

Answer 41

decreases

Question 42

A 1-kg chunk of putty moving at 1 m/s collides with and sticks to a 5-kg bowling ball initially at rest. The bowling ball and putty then move with a momentum of

Answer 42

1 kg m/s.

Question 43

A 2-kg rifle that is suspended by strings fires a 0.01-kg bullet at 200 m/s. The recoil velocity of the rifle is about

Answer 43

1 m/s.

Question 44

A 5000-kg freight car moving at 2 m/s collides with a 10,000-kg freight car at rest. They couple upon collision and move away at

Answer 44

2/3 m/s.

Question 45

A 5000-kg freight car collides with a 10,000-kg freight car at rest. They couple upon collision and move at 2 m/s. What was the initial speed of the 5000-kg car?

Answer 45

6 m/s

Question 46

A red car has a head-on collision with an approaching blue car with the same magnitude of momentum. A green car driving with the same momentum as the other cars collides with an enormously massive wall. Which of the three cars will experience the greatest impulse?

Answer 46

all the same

Question 47

Two vehicles with equal magnitudes of momentum traveling at right angles to each other undergo an inelastic collision. The combined wreck moves in a direction

Answer 47

at 45 degrees to the direction of either car before collision.

Question 48

When a vertically falling firecracker bursts, the vector sum of momentum fragments

Answer 48

- in the horizontal direction cancels to zero. | - in the vertical direction equals the momentum of the firecracker before bursting

Question 49

A cannonball following a parabolic path explodes into fragments. The momentum of the fragments

Answer 49

continue along the path as if the explosion didn't occur

Question 50

``` What is the magnitude of the impulse on an 7.2- kg ball rolling at 3.0 m/s when it bumps into a pillow and stops? ```

Answer 50

22 Ns

Question 51

If a monkey floating in outer space throws his hat away, the hat and the monkey will both

Answer 51

move away from each other, but at different speeds.

Question 52

A 5-kg shark swimming at 1 m/s swallows an absent-minded 1-kg fish swimming toward it at 4 m/s. The speed of the shark after his meal is

Answer 52

1/6 m/s.

Question 53

Two identical objects in outer space, one moving at 2 m/s, the other at 1 m/s, have a head-on collision and stick together. Their combined speed after the collision is

Answer 53

0.5 m/s.

Question 54

Two vehicles with equal magnitudes of momentum traveling at right angles to each other undergo an inelastic collision. The magnitude of momentum for the combined wreck is

Answer 54

greater than the magnitude of momentum of either car before collision.