Kinetic Energy
7.2 Kinetic Energy
Learning Objectives
By the end of this section, you will be able to:
- Calculate the kinetic energy of a particle given its mass and its velocity or momentum
- Evaluate the kinetic energy of a body, relative to different frames of reference
Kinetic Energy
The kinetic energy of a particle is one-half the product of the particle’s mass m and the square of its speed v:
Practice!
| Practice 7.2.1 |
|---|
| You observe two identical balls heading directly toward each other at equal speeds. What can you say about their total kinetic energy? |
| (a) They have some total amount of kinetic energy, with a magnitude between zero and double the kinetic energy of either ball by itself. |
| (b) They have zero total kinetic energy. |
| (c) They have twice the kinetic energy of either ball by itself. |
| (d) Nothing. The kinetic energy of separate objects cannot be combined. |
Discuss!
Consider how you would answer these questions. Then bring this to class for a group discussion.
One particle has mass m and a second particle has mass 2m. The second particle is moving with speed v and the first with speed 2v. How do their kinetic energies compare?
A particle of m has a velocity of 
. Is its kinetic energy given by 
? If not, what is the correct expression?
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