Energy Concepts - Answers
1. Explain how energy and work are related.
Energy is the ability to do work. Work done on an object gives the object potential or kinetic energy.
2. Which type of energy does a wound watch spring have? Potential What kind of energy does a running
mechanical watch use? Kinetic When a watch runs down what happens to the energy? The energy is lost to the
system as heat due to friction.
Can the kinetic energy of a baseball ever be negative? Explain. No. KE = ½ mv2 Velocity is the term that would
have a positive or negative sign. Since velocity is squared it must be positive.
3. Can a baseball have kinetic energy and potential energy at the same time? Certainly if it is moving it has kinetic
energy. If it is some distance above the ground it has gravitational potential energy.
4. Work is required to lift a barbell, how many times as much work is required to lift it 3 times as high? 3 times as
much
5. A compact car and a semi truck are both travelling at the same velocity. Which has more kinetic energy? The
truck has more kinetic energy since it has more mass.
6. Sally and Lisa have identical compact cars. Sally drives on the freeway with a greater speed than Lisa. Which car
has more kinetic energy? Sally has a greater kinetic energy since she has a greater velocity.
7. Sally and Lisa have identical compact cars. Sally is northbound on the freeway and Lisa is southbound with the
same speed. Which car has more kinetic energy? They have the same amount of kinetic energy. Direction
doesn’t matter.
8. Is it possible to exert a force and yet not cause a change in kinetic energy? Yes. If you lean against a car or a wall
and it doesn’t move you are proving that. You are applying a force to an object that is not moving and it still
doesn’t move.
9. If two identical bowling balls are raised to the same height, one on Earth and the other on the moon, which has
larger potential energy relative to the surface of the bodies? The bowling ball on Earth will have a greater
potential energy relative to the surface because the Earth has a much greater mass, and therefore a much
stronger gravitational acceleration.
10. Roads seldom go straight up a mountain but wind around and go up gradually. Explain why this is a good idea.
While a long winding road and shorter more direct one might both get you to the top of a mountain, you will use
less force on the long winding one so it may seem easier. W =Fd
11. What will be the kinetic energy of an arrow shot from a bow having the potential energy of 50 J ? 50 J, the
energy is transfer from the bow string to the arrow.