Let’s see how you did! If you didn’t get a few of these, don’t let it stress you out – it just means you need to play with more experiments in this area. We’re all works in progress, and we have our entire lifetime to puzzle together the mysteries of the universe!
Here’s printer-friendly versions of the exercises and answers for you to print out: Simply click here for K-8 and here for K-12.
Answers:
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1. Potential energy is the energy that something has that can be released.
2. Kinetic energy is the energy of motion. KE = 1/2 mv2
3. Gravitational potential energy is the energy something has due to gravity. Gravitational Potential Energy = mgh.
4. Energy can be changed from one form to another and from one object to another.
5. In a closed system energy can neither be created or destroyed.
6. See below…
7. Potential energy is greatest at a. The coaster is at it’s highest point above the ground.
8. Kinetic Energy is the greatest at c. The coaster is going the fastest at this point.
9. Potential energy is lowest at c. The coaster is as low as it can get.
10. Kinetic energy is lowest at a. The coaster is not moving.
11. KE is increasing and PE is decreasing at b. The coaster is losing height so it’s losing PE but it is gaining speed so it is gaining KE.
12. PE is increasing and KE is decreasing at d. The coaster is getting higher so it’s gaining PE but it’s losing speed so it’s losing KE.
13. Energy efficiency is how much energy in a system is transferred to useless energy.
14. It depends on what you want the car to do! If you want the car to go far after leaving the track you want the brand new one. It will have less of the original potential energy transferred to heat since it will have less friction. However, if you want your car to generate heat, you want the stepped on one. It will have much more of its energy transferred to heat due to its high friction! (In other words, you need to be a bit careful with the term “useful” energy)
15. Sound energy and heat energy. Heat comes from the force of friction. Sound energy, as a matter of fact, also gets transferred to heat energy.
16. Work is defined as moving an object over a distance against a force. Work = force x distance
17. A Newton is a unit of force. How much force it takes to push or pull something. It takes about one Newton of force to lift an apple.
18. A Joule is a unit of energy. It takes one Joule to exert one Newton of force over a distance of one meter.
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Answers for Advanced Students:
19. PE = mgh
PE = 1 kg x 10 m/s2 ft/s2 x 3m
PE = 30 Joules
20. PE = mgh
PE = 1 kg x 10 m/s2 x 2m
PE = 20 Joules (Don’t worry, since the snowball falls apart very little of the energy actually gets transferred to poor Susie.)
21. 20 Joules. All the potential energy that the snowball started with becomes kinetic energy by the time it hits Susie.
22. KE = 1/2 mv2
KE = 1/2 680 kg x (13m/s)2
KE = 340 kg x 169
KE = 57460 Joules (WOW!)
23. KE= 1/2 mv2
KE =1/2 680 x 262
KE = 340 x 676
KE = 229,840 Joules (WOW WOW)
This is an important point. As the speed of something doubles, its kinetic energy squares! This is why it is very important to not speed in a car. An increase in speed quickly increases the potentially dangerous kinetic energy.
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