question

The work that is done when twice the load is lifted twice the distance is

answer

four times as much

question

When one does twice the work in twice the time, the power expended is

answer

the same

question

Two cars are raised to the same elevation on service-station lifts. If one car is twice as massive as the other, compare their gains of potential energy

answer

the car with twice the mass has twice the gain of potential energy

question

What happens the first time Dr. Hewitt lifts the bowling ball near his teeth and lets go?

answer

The ball returns to Dr. Hewitt, stopping almost exactly at the point where it was released.

question

Why does the bowling ball behave the way it does the first time Dr. Hewitt lifts the bowling ball near his teeth and lets go?

answer

All of the initial energy of the ball was converted completely back to potential energy when the ball returned.

question

What happens the second time Dr. Hewitt lifts the bowling ball near his teeth and gives it a push?

answer

The ball leaves Dr. Hewitt and returns to him, going past the point where it was released.

question

Why does the bowling ball behave as it does when Dr. Hewitt lifts it and gives it a push?

answer

The extra energy from the push is converted into kinetic energy, which is then converted into more potential energy at the end of the motion than the ball had when it was released.

question

When you lift twice the load twice as high, in half the time, the increase in potential energy is _______.

answer

four times.

question

When traveling twice as fast your kinetic energy is increased _______.

answer

by a factor of four.

question

Energy cannot be _______.

answer

destroyed.

question

If you push a crate horizontally with 100 N across a 10-m factory floor and the friction between the crate and the floor is a steady 70 N, how much kinetic energy does the crate gain?

answer

300 J

question

Which word in the statement of this problem allows you to assume that the table is frictionless?

answer

smooth

question

Suppose the potential energy of the block at the table is given by mgh/3. This implies that the chosen zero level of potential energy is __________.

answer

a distance 2h/3 above the floor

question

If the zero level is a distance 2h/3 above the floor, what is the potential energy U of the block on the floor?

answer

U = −2mgh/3

question

Considering that the potential energy of the block at the table is mgh/3 and that on the floor is −2mgh/3, what is the change in potential energy ΔU of the block if it is moved from the table to the floor?

answer

ΔU = −mgh

question

Which form of the law of conservation of energy describes the motion of the block when it slides from the top of the table to the bottom of the ramp?

answer

12mv2i+mghi=12mv2f+mghf

question

As the block slides down the ramp, what happens to its kinetic energy K, potential energy U, and total mechanical energy E?

answer

K increases;U decreases;E stays the same

question

As the block slides across the floor, what happens to its kinetic energy K, potential energy U, and total mechanical energy E?

answer

K decreases;U stays the same;E decreases

question

What force is responsible for the decrease in the mechanical energy of the block?

answer

friction

question

Suppose our experimenter repeats his experiment on a planet more massive than Earth, where the acceleration due to gravity is g=30 m/s2. When he releases the ball from chin height without giving it a push, how will the ball's behavior differ from its behavior on Earth? Ignore friction and air resistance. (Select all that apply.)

answer

It will take less time to return to the point from which it was released.

question

What will the kinetic energy of a pile driver ram be if it starts from rest and undergoes a 10 kJ decrease in potential energy?

answer

10KJ

question

When the useful energy output of a simple machine is 100 J, and the total energy input is 200 J, the efficiency is _______.

answer

50%

question

If an input of 100 J in a pulley system increases the potential energy of a load by 60 J, what is the efficiency of the system?

answer

60%

question

Fossil fuels, hydroelectric power, and wind power ultimately get their energy from _______.

answer

the Sun

question

Select the correct equations that show that 7.2 J of work is done when a force of 6.0 N moves a book 1.2 m.

answer

W=F⋅d=(6.0N)⋅(1.2m)=7.2J

question

Calculate the kinetic energy of an 88-kg scooter moving at 12 m/s .

answer

KE= 6300 J

question

If a golf ball and a Ping-Pong ball both move with the same kinetic energy, can you say which has the greater speed? Explain in terms of the definition of KE. Similarly, in a gaseous mixture of heavy molecules and light molecules with the same average KE, can you say which have the greater speed?

answer

If KEs are the same but masses differ, then the ball with smaller mass has the greater speed. That is, 1⁄2Mv^2 = 1⁄2mV^2. Likewise with molecules, where lighter ones move faster on the average than more massive ones.

question

Why is it easier to stop a lightly loaded truck than a heavier one that has equal speed?

answer

It has less kinetic energy so it needs less work to stop

question

What is the unit of work?

answer

joule

question

Which requires more work: lifting a 50-kg sack a vertical distance of 2 m or lifting a 25-kg sack a vertical distance of 4 m?

answer

Both take the same 1000 J.

question

When the speed of a moving car is doubled, how much more kinetic energy does it have?

answer

it has four times as much

question

Can a machine multiply input force? Input distance? Input energy?

answer

Force and distance, but not energy

question

A force of 50 N is applied to the end of a lever, which is moved a certain distance. If the other end of the lever moves one-third as far, how much force does it exert?

answer

150N

question

What is the efficiency of a machine that miraculously converts all the input energy to useful output energy?

answer

100%

question

Scissors for cutting paper have long blades and short handles, whereas metal-cutting shears have long handles and short blades. Bolt cutters have very long handles and very short blades. Why is this so?

answer

Scissors and shears are levers. The applied force is normally exerted over a short distance for scissors so that the output force is exerted over a relatively long distance (except when you want a large cutting force like cutting a piece of tough rope, and you place the rope close to the "fulcrum" so you can multiply force). With metal-cutting shears, the handles are long so that a relatively small input force is exerted over a long distance to produce a large output force over a short distance.

question

On a playground slide, a child has potential energy that decreases by 1000 J while her kinetic energy increases by 900 J. What other form of energy is involved, and how much?

answer

thermal energy AND 100J