physcial science review homework 4

Two identical freight cars roll without friction towards each other on a level track. One car rolls at 2 m/s and the other car rolls at 1 m/s. After the cars collide, they couple and roll together with a speed of

0.5 m/s

a 30 kg girl and a 25 kg boy face each-other on friction free roller blades. The girl pushes the boy, who moves away at a speed of 1.0 m/s. The girls speed is

0.83 m/s

a machine puts out 100 W of power to every 1000 W put into it. The efficiency of the machine is

110%

A ball is moving at 4m/s and has a momentum of 48kg-m/s. What is the balls mass?

12 kg

A car moves 4 times as fast as another identical car. Compared to the slower car, the faster car has

16 times the kinetic energy

A car moving at 50 km/h skids 20 m with locked brakes. How far will it skid if its initial speed is 150 km/h

180 m

exert 100 J in 50 s and your power output is

2 W

A 2 kg mass that weighs 20 N has 40 J of potential energy relative to the ground. What is the height?

2 m

When the input piston of a hydraulic press is depressed 20 cm, the output piston is observed to move 1 cm. An input force of 1 N can raise no more than

20 N

A 1000 kg car moving at 10 m/s that brakes to a stop in 5 s has an average breaking force of

2000 N

A music console is pushed a distance of 2 m with a force of 20 N. The work done on the console is

40 J

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

5 J

A piece of taffy slams into and sticks to another identical piece of taffy that is at rest. The momentum of the two pieces of taffy stuck together after the collision is the same as it was before the collision. Kinetic energy is a different story, for part of it turns into heat. What percentage of the kinetic energy converts into heat?

50%

A diver who weighs 500 N steps off a diving board 10 m above the water with kinetic energy of

5000 J

The ultimate source of energy from fossil fuels is the

Sun

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

a pickup truck speeding along the highway

The massive ram of a pile driver falling from rest strikes a pile with a speed that depends on the

all of the above

Which requires more work; lifting a 50 kg sack vertically 2 m or lifting a 25 kg sack vertically 4 m?

both require the same amount of work

A popular swinging-balls apparatus (newtons cradle) consists of a series of identical elastic balls suspended by strings so they barley touch each other. When two balls are pulled away from one end and released, they strike the row of balls and two balls pop out from the other end. If instead, one ball popped out with twice the speed, this would be a violation of conservation

energy

a simple machine CANNOT multiply 5

energy

which of these forms of energy is NOT renewable?

fossil fuel power

You use a straw for a pea shooter. The speed of the pea emerging from the straw when you blow through it will be greater if the straw is

full length

Compared to a recoiling rifle, the bullet that is fired has a greater

kinetic energy

A ball is projected into the air with 900 J of kinetic energy that is transformed to potential energy at the top of its trajectory. When it returns to its original level after encountering air resistance, its kinetic energy is

less than 900 J

An object may have potential energy because of its

location

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

longer time to stop

A heavy truck and a small truck roll down a hill. Neglecting friction, at the bottom of the hill the heavy truck has greater

momentum

An object in motion will continue in motion with

momentum

A dog and a mouse run along a road with the same kinetic energy. The faster runner is the

mouse

If you push for an hour against a stationary wall, you do no work

on the wall

The source of Earth's internal energy involves

radioactivity

Suppose a gun were made of strong lightweight material with a pellet that is more massive than the gun. Then firing speed is greater for the

recoiling gun

It is correct to say that impulse is equal to

the change in momentum

The most underlying feature of machines is

the conservation of energy

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

the force on the ball is at right angles to the balls motion

a 50 kg sack is lifted 2 m in the same time as a 25 kg is lifted 4 m. The power expended in raising the 50 kg sack compared to the power used to lift the 25 kg sack is

the same

In order to catch a fast-moving softball with your bare hand, you extend your hand foward just before the catch and then let the ball ride backward with your hand. Doing this reduces the catching force because the

time of catch is increased

The distinction between impulse and force involves the

time the force acts

Strictly speaking, if any electrical device in an automobile is turned on (such as an air conditioner, headlights, or radio) more fuel is consumed by the engine. This statement is

true

if you do work on an object in half the time, your power output is

twice

An object lifted 10 m gains a certain amount of potential energy. If it is lifted 20 m, its gain in potential energy is

twice as much

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

twice as much work

the most energy per unit mass can be extracted from

uranium

Recoil is noticeable if we throw a heavy ball while standing on a skateboard. If instead we go through the throwing motion but hold onto the ball, without friction effects our net recoil will be

zero

The conservation of momentum is closely related to

Newtons third law