Chapter 6

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

0

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

1 kg m/s

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

1 m/s

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

1 m/s

A piece of putty moving with 1 unit of momentum strikes and sticks to a heavy bowling ball that is initially at rest. After the putty sticks to the ball, both move with a combined momentum of

1 unit

A piece of putty moving with 1 unit of momentum strikes and sticks to a heavy bowling ball that is initially at rest. Both move with a combined momentum of

1 unit

In the preceding question, what is the total momentum of the balls of putty before and after the collision?

1.41 kg·m/s before and after

A bungee jumper attains a speed of 30 m/s just as the bungee cord begins to stretch. If the period of stretch is 2 s, the magnitude of the jumper's average deceleration is about

1.5 g

Two identical gliders slide toward each other on an air track. One moves at 1 m/s and the other at 2 m/s. They collide and stick. The combined mass moves at

1/2 m/s

Two identical gliders slide toward each other on an air track. One moves at 1 m/s and the other at 2 m/s. They collide, stick, and moves at

1/2 m/s

A 1-kg glider and a 2-kg glider both slide toward each other at 1 m/s on an air track. They collide and stick. The combined mass moves at

1/3 m/s

A 1-kg chunk of putty moving at 1 m/s collides with and sticks to a 5-kg bowling ball that is initially at rest on a frictionless surface. The speed of the putty thereafter is

1/6 m/s

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

1/6 m/s

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

1/6 m/s

Consider massive gliders that slide friction-free along a horizontal air track. Glider A has a mass of 1 kg, a speed of 1 m/s, and collides with Glider B that has a mass of 5 kg and is at rest. If they stick upon collision, their speed after collision will be

1/6 m/s

A ball is moving at 3 m/s and has a momentum of 48 kg m/s. What is the ball's mass?

16 kg

A 5000-kg freight car moving at 2 m/s runs into a 10,000-kg freight car at rest. They couple upon collision and move away as one body at

2 m/s

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

2/3 m/s

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

2000 N

A 3.6-kg chihuahua charges at a speed of 3.3m/s. What is the magnitude of the average force needed to bring the chihuahua to a stop in 0.50s?

24 N

A 4 kg ball has a momentum of 12 kg m/s. What is the ball's speed?

3 m/s

A 1700kg rhino charges at a speed of 50.0km/h. What is the magnitude of the average force needed to bring the rhino to a stop in 0.50s?

4.7×10^4 N

A 5-kg fish swimming at 1 m/s swallows an absent-minded 1-kg fish at rest. The speed of the larger fish after lunch is

5/6 m/s

A 5-kg fish swimming at a speed of 1 m/s swallows an absent-minded 1-kg fish at rest. The speed of the larger fish after this lunch is

5/6 m/s

Two 5000-kg rail cars roll without friction (one at 1 m/s, the other at 2 m/s) toward each other on a level track. They collide, couple, and roll together with a combined momentum of

5000 kg m/s

The change in momentum, in kg m/s, that occurs when a 1.0 kg ball travelling at 4.0 m/s strikes a wall and bounces back at 2.0 m/s is

6

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

6 m/s

If the object has a mass of 5.0kg and is at rest at t=0s, how fast is the object moving at t=4.0s?

7.2 m/s

If all people, animals, trains and trucks all over the world began to walk or run towards the east, then the

Earth would spin a bit slower.

A car carrying a 78-kg test dummy crashes into a wall at 29 m/s and is brought to rest in 0.10 s. What is the magnitude of the average force exerted by the seat belt on the dummy?

F = 2.3 x 10^4 N

Joanne drives her car with a mass of 1000 kg at a speed of 25 m/s. What is the magnitude of road friction force that is needed to bring her car to a halt in 9.0 s?

F = 2800 N

How much impulse stops a 50-kg carton sliding at 4.8 m/s when it meets a rough surface?

J = 240 N⋅s

When you are struck by a moving object, is it favorable that the object makes contact with you over a short time or over a long time?

Long contact time decreases the magnitude of the average force and is favorable.

The impulse-momentum relationship is a direct result of

Newton's 2nd Law

The conservation of momentum is most closely related to

Newton's 3rd law

A large heavy truck and a small baby carriage roll down a hill. Neglecting friction, at the bottom of the hill, the baby carriage will have a greater

None of these (speed, momentum, acceleration)

Why is it advantageous to roll with the punch in boxing?

Rolling with the punch increases contact time, which decreases the force

Why is a force that is applied for a short time more effective in karate?

The average force is increased.

Which statement must be true for the momentum of a system to be conserved?

The net external force on the system is zero. When the net external force on a system is zero, the system has zero acceleration and constant momentum.

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?

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

Two automobiles, each of mass 900 kg , are moving at the same speed, 25 m/s , when they collide and stick together. In what direction and at what speed does the wreckage move if one car was driving north and one south.

The wreckage after collision is motionless.

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

a pickup truck speeding along a highway

When you jump from an elevated position you usually bend your knees upon reaching the ground. By doing this, you make the time of the impact about 10 times as great as for a stiff-legged landing. In this way the average force your body experiences is

about 1/10 as great

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

about 1/10 as great.

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

acceleration

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

at 45 degrees to the direction of either car before collision

Which would produce more force: driving into a very massive concrete wall with no "give," or having a head-on collision at the same speed with an identical car moving toward you with the same speed?

both the same

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?

both the same

The greater efficiency achieved with the curved blades of a Pelton wheel is due to

bouncing

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

doubled

According to the impulse-momentum equation Ft = change in (mv), a person will suffer less injury falling on a wooden floor which "gives" than on a more rigid cement floor. The "F" in the above equation stands for the force exerted on the

either the force on the person or the force on the floor

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

equal and opposite to the momentum of the fired cannonball

The force that accelerates a rocket in outer space is exerted on the rocket by the

exhaust gases

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 to the force that stops the car, the force needed to stop the truck is

greater

Momentum is transferred to the ground when an apple falls on it. The momentum absorbed by the ground is

greater than that of the apple only if the apple bounces

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

greater with the brick wall

Cassy can get more force on the bricks she breaks with a blow of her bare hand when _______.

her hand is made to bounce from the bricks.

A karate expert executes a swift blow and breaks a cement block with her bare hand. The magnitude of the force experienced by her hand is

identical to the force applied to the block.

A bullet is fired from a gun. The speed of the bullet will be about the same as the speed of the recoiling gun

if the mass of the bullet equals the mass of the gun

Compared to the force that brings a small car to a stop, the force required to bring a heavy truck to a stop

impossible to determine without additional information

Follow through is important in golf because it results in a greater _______.

impulse on the ball

A softer landing occurs when an falling object bounces from a surface

in an extended time.

When a boxer moves into an oncoming punch, the force experienced is

increased

Padded dashboards in cars are safer in an accident than nonpadded ones because an occupant hitting the dash has

increased time of impact

An impulse can be increased by

increasing the force or increasing the time interval.

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

its mass times velocity is greater than that of the car

When you are in the way of a fast-moving object and can't get out of its way, you will suffer a smaller force of impact if you decrease its momentum over a

long time

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

longer time

Two objects have the same size and shape, but one is much heavier than the other. When they are dropped simultaneously from a tower, they reach the ground at the same time, but the heavier one has a greater

momentum

A large metal ball is shot from a cannon with a short barrel. If the same ball were to be shot from cannon with a longer barrel, its muzzle velocity would be

more

A car traveling along the highway needs a certain amount of force exerted on it to stop it in a certain distance. More stopping force is required when the car has

more mass, more momentum, less stopping distance

A golf ball moving forward with 1 unit of momentum strikes and bounces backward off a heavy bowling ball that is initially at rest and free to move. The bowling ball is set in motion with a momentum of

more than 1 unit

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

move away from each other, but at different speeds

An astronaut , floating alone in outer space, throws a baseball. If the ball floats away at a speed of 20 meters per second, the astronaut will

move in the opposite direction, but at a lower speed

A fan attached to an ice sailcraft stalled on a windless day blows air into the sail that bounces backward upon impact. The boat

moves in the direction of the wind impact force

A 1-N apple falls to the ground. The apple hits the ground with an impact force of about

not enough information given to say

What is the momentum of a 42-kg carton that slides at 4.4 m/s across an icy surface?

p = 180 kg⋅m/s

What impulse occurs when an average force of 11 N is exerted on a cart for 2.4 s ?

p = 26 kg⋅m/s

A rifle recoils while firing a bullet. The speed of the rifle's recoil is small because the

rifle has much more mass than the bullet

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

stopping time is longer on the carpet

It is correct to say that impulse is equal to

the change in momentum it produces

When a cannonball is fired, the momentum of the system (cannon + cannonball) is conserved if

the momentum of the cannon is equal to the magnitude of the momentum of the cannon ball and points in the opposite direction.

A karate expert executes a swift blow and breaks a cement block with her bare hand. The magnitude of the force on her hand is

the same as the force applied to the block

The force on an apple hitting the ground depends upon

the speed of the apple just before it hits, the time of impact with the ground, whether or not the apple bounces.

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

the target would be safer than the shooter.

A fan attached to an ice sailcraft stalled on a windless day blows air into the sail that bounces backward upon impact. The boat can

then move in the direction of the wind impact force.

To catch a ball, a baseball player extends the hand forward before impact with the ball and then lets it ride backward in the direction of the ball's motion. Doing this reduces the force of impact on the player's hand principally because the

time of impact is increased

In what direction does the wreckage move if one car was driving north and one east (as shown in the following figure)

to the northeast

Two automobiles, each of mass 900 kg , are moving at the same speed, 25 m/s , when they collide and stick together. At what speed does the wreckage move if one car was driving north and one east?

v = 18 m/s

A railroad diesel engine weighs four times as much as a freight car. If the diesel engine coasts at 5.8 km/h into a freight car that is initially at rest, find the speed of the coupled cars.

v = 4.6 km/h

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

vectorally add up to equal the initial momentum of the firecracker

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?

yes, always

Recoil is noticeable if we throw a heavy ball while standing on roller skates. If instead we go through the motions of throwing the ball but hold onto it, our net recoil will be

zero