Hydroelectric energy comes from gravity pulling down water through dams in rivers. Explain how such energy is really just a form of solar energy by tracing how the sun's energy is able to get the water from the ocean to the reservoir behind the dam.

An advertisement for a portable electrical generating unit claims that the unit's diesel engine produces $28,000 \mathrm{hp}$ to drive an electrical generator that produces $30 \mathrm{MW}$ of electrical power. Is this possible? Explain.

A woman bounces on a trampoline, going a little higher with each bounce. Justify how she increases the total mechanical energy.

If a projectile is fired upward at various angles above the horizontal, it has the same initial kinetic energy in each case. Why does it not then rise to the same maximum height in each case?

An elevator is hoisted by its cables at constant speed. Is the total work done on the elevator positive, negative, or zero? Explain.

When you use a jack to lift a car, the force you exert on the jack is much less than the weight of the car. Does this mean that less work is done on the car than if the car were lifted directly?

A rope tied to a body is pulled, causing the body to accelerate. But according to Newton’s third law, the body pulls back on the rope with a force of equal magnitude and opposite direction. Is the total work done then zero? If so, how can the body’s kinetic energy change? Explain.

Can the $\textit{total}$ work done on an object during a displace- ment be negative? Explain. If the total work is negative, can its magnitude be larger than the initial kinetic energy of the object? Explain.

A person on a trampoline can go higher with each bounce. How is this possible? Is there a maximum height to which the person can go?

Why is biomass a better alternative to oil?

A. Biomass does not release carbon dioxide.

B. Biomass creates radioactive waste.

C. Biomass does not need to be burned.

D. Biomass is a renewable resource.

True or false? If hydrogen molecules and oxygen molecules have the same kinetic energy, then they have the same speed. Explain your answer.

How does a lettuce spinner remove water from lettuce?

What is wrong with this statement? "A satellite stays in or because the outward centrifugal force just balances the inward centripetal force." Make a free-body diagram of the satellite.

How does friction produce internal energy? Explain what is happening at the molecular level to produce this form of energy.