question

A 2-kg ball is moving with a speed of 4 m/s, and a 4-kg ball is moving with a speed of 2 m/s. What can you conclude about the kinetic energies of the two balls?

answer

The 2-kg ball has more kinetic energy.

question

A ball is dropped from a distance 5 m above the ground, and it hits the ground with a certain speed. If the same ball is dropped from a distance 10 m above ground, its final speed will be ________.

answer

1.4 times as fast

question

An object is dropped from a distance of R=2REarth from Earth's center, and it falls down and hits Earth's surface. If the object is dropped from a distance R=3REarth (twice as far away from Earth's surface), its kinetic energy right before hitting the ground would be _____ what it was before.

answer

greater than the original value but less than twice

question

If an object had a temperature of absolute zero (0 K), its ______________.

answer

thermal energy would be zero

question

A star forms when gravity causes a gas cloud to collapse. As the size of the cloud decreases, the temperature of the cloud _____________.

answer

increases

question

A positron is a particle similar to an electron, but with the opposite charge of an electron. If a positron and an electron collide, sometimes both the electron and positron disappear (annihilate), and two photons are created. This is an example of ____________.

answer

the conversion of rest-mass energy into radiative energy

question

A gas containing both hydrogen molecules (each molecule contains two hydrogen atoms) and helium atoms has a temperature of 300 K. How does the average speed of the hydrogen molecules compare to the helium atoms?

answer

The average speed of the hydrogen molecules is faster than that of the helium atoms, but it is less than two times faster.

question

What is the unit of work?

answer

joule

question

A force sets an object in motion. When the force is multiplied by the time of its application, we call the quantity impulse, and an impulse changes the momentum of that object. What do we call the quantity force multiplied by distance?

answer

Work

question

How much work is done on a satellite in a circular orbit about Earth?

answer

Zero

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

Exactly what is it that enables an object to do work?

answer

Energy

question

If both sacks in the preceding question are lifted their respective distances in the same time, how does the power required for each compare? How about for the case in which the lighter sack is moved the same distance in half the time?

answer

Lifted in the same time, the power is the same. The light sack moving in half the time requires double the power.

question

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

answer

four times as much.

question

A car is raised a certain distance in a service-station lift, thus giving it potential energy relative to the floor. If it were raised twice as high, how much more potential energy would it have?

answer

It would have twice as much potential energy.

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 potential energy.

question

When is the potential energy of something significant?

answer

When the potential energy changes

question

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

answer

the same.

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

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 four.

question

Compared with a car moving at some original speed, how much work must the brakes of a car supply to stop a car that is moving twice as fast? How will the stopping distances compare?

answer

It takes four times the work and four times the stopping distance.

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

300J

question

How does speed affect the friction between a road and a skidding tire?

answer

Speed has no effect on the friction.

question

Energy cannot be _______.

answer

destroyed

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

10 kJ

question

An apple hanging from a limb has potential energy because of its height. If it falls, what becomes of this energy just before it hits the ground? When it hits the ground?

answer

The energy is kinetic energy before it hits the ground; it is thermal energy after.

question

What is the source of energy in sunshine?

answer

Thermonuclear fusion energy

question

What is recycled energy?

answer

Reused energy that otherwise would be wasted

question

In a simple machine, how much work is done when an input of 10 N acts over a distance of 5 m?

answer

50 J

question

Work

answer

Force x Distance

question

Work energy theorem

answer

Wtotal = 1/2mvf^2 - 1/2mvi^2

question

Net force

answer

Work / distance

question

Power

answer

time it takes to do work, W/delta t

question

units of power

answer

j/s or watts

question

unites of work

answer

joules

question

kilowatts

answer

1 kw = 1000 watts = 1000 j/s

question

GPE

answer

work done by gravity, mgh

question

EPE

answer

spring energy, 1/2kx^2

question

3 laws of work

answer

you can't win, you can't break even, you are a loser

question

the 6 simple machines

answer

screw
pulley
lever
ramp
wheel & axel
wedge

question

IMA

answer

factor by which your force gets reduced (ideal), distance effort/distance resistance

question

MA

answer

accounts for friction (real)
force resistance / force effort