Physics Unit 7

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

Two identical objects in outer space have a head-on collision and stick together. If, before the collision, one had been moving at 2 m/s and the other at 1 m/s, their combined speed after the collision would be

0.5 m/s

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

Which of the following has the largest momentum relative to the Earth?

a pickup truck speeding along a highway

If the net external force acting on a system is zero, then the total momentum of the system is __________.

conserved

An inelastic object __________.

deform upon collsion

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

earth would spin slower

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

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

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

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

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

When an object is in motion, which of the following could not have a value of zero?

none of these could be zero

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

2000 N.

Express 0.000543 in exponential notation.

5.43 x 10-4

Mr. Fretias (83.0 kg) thinks he's Spiderman and decides to jump off of the second floor of Konia. He is traveling at about 9.81 m/s right before he hits the ground and his time of impact with the ground is on 0.150 s. With what average force does he hit the ground?

5430 N

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

Koa and Kai jump off the roof of their house. Koa lands flat on the pavement below while Kai bounces back at the same speed as he hits the pavement. Who is more likely to get hurt?

Kai because he absorbs twice the impulse

The conservation of momentum is most closely related to

Newton's 3rd law.

The impulse-momentum relationship is a direct result of

Newtons 2nd law

A moving object has

all of these

A ball is thrown straight up. At the top of its path what is its acceleration?

about 10 m/s/s

If several balls are thrown straight up with varying initial velocities, the quantity that will have the same value for each trial is the ball's

acceleration

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

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

decreases

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.

If an object has kinetic energy, then it also must have

momentum

A Ping-Pong gun, initially at rest, fires a ball which is at rest. After the shot, the sum of the gun's and ball's __________.

momentum is zero

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 golf ball is thrown at and bounces backward from a massive bowling ball that is initially at rest. After the collision, compared to the golf ball, the bowling ball has

more momentum, but less kinetic energy

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 shorter on the carpet

Which has more momentum, a sports car moving at 30 mph or the same sports car moving at 60 mph?

the car moving at 60 mph

It is correct to say that impulse is equal to

the change in momentum

Compared to the recoiling rifle, the bullet fired has

a greater kinetic energy

What is one difference between a hypothesis and a theory?

a hypothesis is a guess that has not been well tested, whereas a theory is a synthesis of well-tested and verified guesses

When a rifle is fired it recoils as the bullet is set in motion. The rifle and bullet ideally acquire equal

but opposite amounts of momentu

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

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

exhaust gases

The total momentum of a flock of identical birds could be zero only if the birds are

flying in different directions.

Newton's Third Law states that __________.

for every action, there is an equal and opposite reaction

If the speed of a moving object doubles, which of the following also doubles?

momentum

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 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

Two identical freight cars roll without friction (one at 1 m/s, the other at 2 m/s) toward one another on a level track. They collide, couple together, and roll away in the direction that

the faster car was initially going.

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

Suppose an object is in free fall. Each second the object falls __________.

a greater distance than in the second before

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

In order 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.

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

0

What is the acceleration of a vehicle that travels at a steady speed of 30 km/hr for 3 seconds?

0 km/hr/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 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

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

3 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

A piece of taffy slams into and sticks to another identical piece of taffy that is at rest. The momentum of the two pieces stuck together after the collision is the same as it was before the collision, but this is not true of the kinetic energy, which is partly turned into heat. What percentage of the kinetic energy is turned into heat?

50 %

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

5000 kg m/s

A feather and a coin dropped in a vacuum fall with equal

accelerations

A heavy and a light object released from the same height in a vacuum have equal

accelerations

The acceleration produced by a net force on an object is __________.

all answers are correct

If the momentum of an object changes and its mass remains constant, what else is happening to the object?

all of the above

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

all of these

The force on an apple hitting the ground depends upon

all of these

A car has a head-on collision with another car that was approaching with the same magnitude of momentum. A third identical car driving with the same speed as the first car runs into an enormously massive wall. Which of the four objects will experience the greatest impulse?

all will receive the same impulse

An astronaut, floating in space, throws a ball as massive as herself toward her nearby spaceship. If the ball bounces back toward her without losing speed, her best choice at that time is to

hope that the spaceship pilot is able to rescue her somehow

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

impossib le to determine without additional information

Which would be more damaging, 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?

impossib le to determine without additional information

The momentum change of an object is equal to the __________.

impulse acting on the object

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

increased time of impact

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.

A 1-kg ball dropped from a height of 2 m rebounds only 1.5 m after hitting the ground. The amount of energy converted to heat is about

more than 2.0 J.

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 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

A sandbag is motionless in outer space. A second sandbag with 3 times the mass moving at 12 m/s collides with it. They stick together and move at a speed of

none of these

Which has more momentum, a heavy truck moving at 30 mph or a light truck moving at 30 mph?

the heavy truck

A sandbag in outer space moving at 3 m/s and collides and sticks to a half-as-massive sandbag initially at rest. Compared with the kinetic energy of the moving bag before collision, the kinetic energy of the coupled bags after collision is

the same

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

The horizontal component of a projectile's velocity is independent of __________.

the vertical component of its velocity

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

The momentum of a system of bodies is NOT conserved when __________.

there is an external force applied to the system

The difference between impulse and impact force involves the

time the force acts

A student throws an egg at a bed sheet held by two other students. The egg does not break as it would when hitting a wall because __________.

ts time of impact is greater when hitting the bed sheet

For a constant force, if the duration of impact upon an object is doubled, by how much is the resulting change in momentum increased?

twice

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