##### Practice Test 2

If the polar icecaps melted, the resulting water would spread over the entire Earth. This new mass distribution would tend to make the length of a day

A) longer.

B) shorter.

C) stay the same.

D) shorter at first, then longer.

E) longer at first, then shorter

A) longer.

A huge rotating cloud of particles in space gravitate together to form an increasingly dense ball. As it shrinks in size, the cloud

A) rotates faster.

B) rotates slower.

C) rotates at the same speed.

D) cannot rotate.

A) rotates faster.

If the Earth rotated more slowly about its axis, your apparent weight would

A) increase.

B) decrease.

C) stay the same.

D) be zero.

A)Increase.

To kick a football so it won't topple end over end, kick it so the force of impact extends

A) above its center of gravity.

B) through its center of gravity.

C) below its center of gravity.

B) through its center of gravity.

A tightrope walker more easily balances on a tightwire if his pole

A) is held high.

B) droops.

C) is short but heavy.

B) droops.

The long, heavy tail of a spider monkey enables the monkey to easily vary its

A) weight.

B) momentum.

C) inertia.

D) center of gravity.

E) none of these

D) center of gravity.

The famous Leaning Tower of Pisa doesn't topple over because its center of gravity is

A) above a place of support.

B) relatively low for such a tall building.

C) stabilized by its structure.

D) displaced from its center.

E) in the same place as its center of mass.

A) above a place of support.

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

A) 0.5 m/s.

B) 0.33 m/s.

C) 0.67 m/s.

D) 1.0 m/s.

E) none of these

A) 0.5 m/s.

Compared to the recoiling rifle, the bullet fired has

A) a greater momentum.

B) a greater kinetic energy.

C) a smaller speed.

D) all of the above

B) a greater kinetic energy.

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

A) increases.

B) decreases.

C) doesn't change.

D) cannot be determined with the information given

B) decreases.

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

A) weights.

B) momenta.

C) kinetic energies.

D) accelerations.

E) none of the above

D) accelerations.

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

A) impulse.

B) momentum.

C) acceleration.

D) force.

E) none of these

B) momentum.

A moving object has

A) speed.

B) velocity.

C) momentum.

D) energy.

E) all of these

E) all of these

Whereas impulse involves the time that a force acts, work involves the

A) distance that a force acts.

B) time and distance that a force acts.

C) acceleration that a force produces.

A) distance that a force acts.

A car's engine is 20% efficient. When cruising, the car encounters an average retarding force of 1000 N. If the energy content of gasoline is 40 megajoules per liter, how many kilometers per liter does the car get?

A) 14

B) 12

C) 10

D) 8

E) none of these

D) 8

40,000,000/1000 = 40,000

40,000 m / 1000 = 40 km / L

40 * .20

8

How many Joules of energy are in one kilowatt-hour?

A) 1

B) 60

C) 60,000

D) 3.6 million

E) none of these

D) 3.6 million

1 joule = 1 Watt for 1 second.

60 seconds * 60 minutes = 3600 joules in watt-hour

3600 * 1000

3,600,000 joules in a kilowatt-hour

The ball rolling down an incline has its maximum potential energy at

A) the top.

B) a quarter of the way down.

C) halfway down.

D) the bottom.

A) the top.

An object may have potential energy because of its

A) speed.

B) acceleration.

C) momentum.

D) location.

E) none of these

D) location.

A 1000-kg car and a 2000-kg car are hoisted the same distance. Raising the more massive car requires

A) less work.

B) as much work.

C) twice as much work.

D) four times as much work.

E) more than four times as much work.

C) twice as much work.

If you push an object a given distance, while applying twice the force, you do

A) twice as much work.

B) four times as much work.

C) the same amount of work.

D) half as much work.

A) twice as much work.

If you push for a half hour or a whole hour against a stationary wall

A) no work on the wall is done in either case.

B) half as much work is done during the half hour.

C) twice as much work is done during the half hour.

D) it is impossible to determine how much work is done.

A) no work on the wall is done in either case.

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

A) move away from each other, but at different speeds.

B) move away from each other at the same speed.

C) move a short distance and then slow down.

D) move a short distance and then go faster.

E) come to a stop after a few minutes.

A) move away from each other, but at different speeds.

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

A) negligible compared to the momentum of the apple.

B) greater than that of the apple only if the apple bounces.

C) greater than that of the apple in all cases.

D) none of these

B) greater than that of the apple only if the apple bounces.

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

A) 1/2 m/s.

B) 1/5 m/s.

C) 1/6 m/s.

D) 2/3 m/s.

E) 3/2 m/s.

C) 1/6 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

A) 0.001 m/s.

B) 0.01 m/s.

C) 0.1 m/s.

D) 1 m/s.

E) none of these

D) 1 m/s.

m1v1 = m2v2

.01*200 = 2 * ?

.01*200/2

2/2 = 1

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

A) less.

B) more.

C) the same.

D) impossible to determine without additional information.

B) more.

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

A) 0 kg m/s.

B) 1 kg m/s.

C) 2 kg m/s.

D) 5 kg m/s.

E) more than 5 kg m/s.

B) 1 kg m/s

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

A) zero.

B) less than the force applied to the cement block.

C) identical to the force applied to the block.

D) more than the force applied to the block.

E) impossible to predict without additional information

C) identical to the force applied to the block.

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

A) greater.

B) smaller.

C) the same.

A) greater.

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

A) 4 kg

B) 12 kg

C) 16 kg

D) 144 kg

E) none of these

C) 16 kg

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

A) increased time of impact.

B) decreased time of impact.

C) decreased impulse.

D) increased momentum.

A) increased time of impact.

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

A) less than 1/10 as great.

B) more than 1/10 as great.

C) about 1/10 as great.

D) about 10 times as great.

C) about 1/10 as great.

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

A) speed.

B) acceleration.

C) momentum.

D) all of these

E) none of these

E) none of these

The difference between impulse and impact force involves the

A) difference between acceleration and velocity

B) distance the force acts

C) mass and its effect on resisting a change in momentum

D) time the force acts

D) time the force acts

It is correct to say that impulse is equal to

A) velocity multiplied by time

B) momentum

C) the force multiplied by the distance the force acts

D) the change in momentum

D) the change in momentum

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

A) force against the rifle is smaller than against the bullet

B) momentum of the rifle is smaller

C) rifle has much more mass than the bullet

C) rifle has much more mass than the bullet

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

A) conservation of momentum would not hold

B) the target would be safer than the shooter

C) recoil problems would be lessened

B) the target would be safer than the shooter

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

A) time of impact is decreased

B) time of impact is increased

C) relative velocity is less

B) time of impact is increased

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

A) 48 m/s

B) 4 m/s

C) 3 m/s

D) 12 m/s

C) 3 m/s

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

A) the same as before

B) small but noticeable

C) zero

C) zero

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

A) rocket's wings

B) atmospheric pressure

C) rocket's nose cone

D) exhaust gases

D) exhaust gases

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

A) twice the sum of their original momentums

B) half the sum of their original momentums

C) zero

C) zero

Because the are no external forces, total momentum is conserved. The inital momentum will equal the final momentum. Let m1 be the momentum of 1 and m2 the momentum of the other. Because they are rolling towards one other, the total momentum is

having the same mass and speed roll

m1 - m2 = 0

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

A) 5000N

B) 4000N

C) 2000N

D) 3000N

E) 1000N

C) 2000N

=(1000*10)/5

=10,000/5

=2000

A 6-kg shark swimming at a speed of 8 m/s swallows an absent-minded 2-kg fish swimming 4 m/s in the opposite direction. The speed of the shark after this lunch is

A) 4 m/s

B) 3 m/s

C) 8 m/s

D) 5 m/s

D) 5 m/s

Add the momentums of the fish and then divide by the masses.

p=mv

[(m1*v1) + (m2*v2)]/(m1+m2)

[(6*8)+(2*-4)]/(6+2)

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?

A) the bug

B) the car

C) both the same

C) both the same

Change in momentum is also known as "impulse"... and described by the equation Impulse = ΔFΔt, where F is force and t is time.

According to Newton's laws, both the car and the bug experience the same force (F = ma, since the masses are so different, the acceleration will be also... and the force is always the same for both objects in a collision). They also both experienced the same change in time, as one part of the collision can't have different Δt than another part. Since both change in force, and change in time are the same, so is the impulse, and therefore the change in momentum :]

If you push an object twice as far while applying the same force, you do

A) four times as much work.

B) twice as much work.

C) half as much work.

D) the same amount of work.

B) twice as much work.

A job is done slowly, while an identical job is done quickly. Both jobs require the same amount of work, but different amounts of

A) energy

B) power

C) effort

B) power

If an object is raised twice as high, its potential energy will be

A) half as much

B) twice as much

C) the same

D) four times as much

B) twice as much

An object that has kinetic energy must be

in an elevated position

A) moving

B) falling

C) at rest

A) moving

A bow is drawn so that it has 40 J of potential energy. When fired, the arrow will ideally have a kinetic energy that is

A) less than 40J

B) 40J

C) more than 40J

B) 40J

When a car is braked to a stop, its kinetic energy is transformed to

A) heat

B) stopping energy

C) potential energy

D) energy of rest

A) heat

it changes to potential energy

in some cases yes it will convert back to potential energy... however in this cases when dealing with a car the brakes apply friction which causes heat that eventually brings the car to a stop therefore when completely stopped the kinetic energy will be transformed into heat.

A block of ice sliding down an incline has its maximum speed at

A) the top

B) the same everywhere

C) the bottom

C) the bottom

No work is done by gravity on a bowling ball that rolls along a bowling alley because

A) no distance is covered by the ball.

B) no force acts on the ball.

C) the force on the ball is at right angles to the ball's motion.

C) the force on the ball is at right angles to the ball's motion.

'Work' is only done by a force if the speed of an object changes because of that force.

a. is a filler answer to make up the number of 4.

b. nice but incorrect. Gravity and repulsion (from the floor) both act on the ball but they are in perfect balance. But you can't say they don't act.

Gravity is not changing the speed of the ball because it is not acting in the direction of it's motion.

work is dependant on displacement.

there is no dispacement in the y direction. ( The ball only moves in the x direction) Therefore no work is done by gravity.

A TV set is pushed a distance of 2 m with a force of 20 N. How much work is done on the set?

A) 40J

B) 18J

C) 10J

D) 400J

A) 40J

W = Fd

Work = Force x displacement

A car that travels twice as fast as another when braking to a stop will skid

A) the same distance

B) four times as far

C) twice as far

B) four times as far

KE increases by the square of the velocity, so double the speed and the KE is 4 times greater.

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

A) impulse

B) acceleration

C) force

D) momentum

D) momentum

A bullet has more kinetic energy than the recoiling rifle from which it is fired is because the force on the bullet acts over a

A) longer time

B) longer distance

B) longer distance

Horses that move with the fastest linear speed on a merry-go-round are located

A) near the outside

B) near the center

C) they all move at the same speed

A) near the outside

If you replace the wheels and tires of your car with new ones having greater diameters, all of your speedometer readings thereafter will

A) decrease

B) remain the same

C) increase

A) decrease

When a train makes a curve, the wheels squeal because different parts of the wheel rims

A) must all contract at the same time.

B) try to cover a different distance in the same time.

C) vibrate at different rates.

B) try to cover a different distance in the same time.

Suppose the circumference of a bicycle wheel is 2 meters. If it rotates at 1 revolution per second when you are riding the bicycle, then your speed will be

A) 3 m/s

B) 1 m/s

C) 3.14 m/s

D) 2 m/s

D) 2 m/s

An industrial flywheel has a greater rotational inertia when most of its mass is

A) uniformly distributed

B) near the center

C) near the outer edge

C) near the outer edge

A coin and a ring roll down an incline starting at the same time. The one to reach the bottom first will be the

A) ring

B) both reach at the same time

C) coin

C) coin

On a balanced see saw, a boy three times as heavy as his partner sits

A) 1/9 the distance from the fulcrum.

B) three times the distance from the fulcrum.

C) 1/3 the distance from the fulcrum.

D) nine times the distance from the fulcrum.

C) 1/3 the distance from the fulcrum.

Put a pipe over the end of a wrench when trying to turn a stubborn nut on a bolt, to effectively make the wrench handle twice as long, you'll multiply the torque by

A) four

B) two

C) six

D) eight

B) two

Toss a baseball bat into the air and it wobbles about its

A) heavier end

B) center of mass

C) geometrical center

B) center of mass

The chef at the infamous Fattening Tower of Pizza tosses a spinning disk of uncooked pizza dough into the air. The disk's diameter increases during the flight, while its rotational speed

A) increases

B) decreases

C) remains the same

B) decreases

For a system in mechanical equilibrium,

A) the forces equal the torques.

B) the net forces and torques must both be zero.

C) acceleration is negative

B) the net forces and torques must both be zero.

Suppose you're on a Ferris wheel at a carnival, seated 15 m from the Ferris wheel's axis. If you make a complete rotation each minute, your linear speed is

A) 3.14 m/s

B) 1.57 m/s

C) 15 m/s

D) .25 m/s

B) 1.57 m/s

one turn is a distance of 2piR = 2pi*15 m

the time needed for 1 turn is 1 min = 60 s

use v = s/t for the velocity

v = 2pi*15/60 = 1.57 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

A) 0.001 m/s.

B) 0.01 m/s.

C) 0.1 m/s.

D) 1 m/s.

E) none of these

D) 1 m/s.

m1 = 2 kg

v1 = ?

m2 = 0.01 kg

v2 = 200 m/s

Set it up as a conservation of momentum problem

m1v1 = m2v2

Insert values and solve for v1

(2 kg) * v1 = (0.01 kg) * (200 m/s)

(2 kg) * v1 = (2 kg-m/s)

v1 = (2 kg-m/s) / (2 kg)

v1 = 1 m/s

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

A) a tightrope walker crossing Niagara Falls

B) a pickup truck speeding along a highway

C) a Mack truck parked in a parking lot

D) the Science building on campus

E) a dog running down the street

B) a pickup truck speeding along a highway