Chapter 7

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?

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 ________.

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.

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

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

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 ____________.

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?

What is the unit of work?

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?

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

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?

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

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?

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

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?

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.

When is the potential energy of something significant?

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

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

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

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

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?

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?

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

Energy cannot be _______.

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?

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?

What is the source of energy in sunshine?

What is recycled energy?

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

Work

Work energy theorem

Net force

Power

units of power

unites of work

kilowatts

GPE

EPE

3 laws of work

the 6 simple machines

IMA

MA