Question

Two objects, A and B, each of mass 0.22 kg, are moving at 0.52 m/s directly toward each other. A completely inelastic collision occurs and both objects stop. What percentage of the total kinetic energy is changed into other forms of energy

Answer 1

Do you know the equation for kinetic energy?

Answer 2

yes, 1/2MV^2

Answer 3

The problem tells you both objects stop. What can you conclude from that?

Answer 4

i'm not sure:/

Answer 5

If they aren't moving, they have no velocity (v=0). What does that tell you about the kinetic energy?

Answer 6

there is no kinetic energy?

Answer 7

Right. If you plug 0 into the v value in the kinetic energy equation, no matter what the mass is or anything else, there is no kinetic energy. If you have no kinetic energy anymore, how much of it went to different forms? Don't overthink it.

Answer 8

okay thank you! the options are 0 percent, 25 percent, 50 percent, and 100 percent.
So the answer is 0 percent?

Answer 9

Reread the question carefully:
"What percentage of the total kinetic energy is changed into other forms of energy?"

If you have a tank of gas in your car and use it all up and now you're on empty, did you use 0%?

Answer 10

no, I used all of it. so 100percent?

Answer 11

You start out with some initial kinetic energy. Now you have none. So how much of yoru kinetic energy disappeared?

Answer 12

Exactly. You used all of it: 100%.

Answer 13

Thank you!!

Answer 14

No problem! Let me know if you need any more help.

Answer 15

I did have one other question. Which of these is the best example of an elastic collision?
A rubber ball is dropped from 1.2m and bounces back up to a height of 0.8m.
A billiard ball strikes another of the same mass at rest and stops, and the second ball then moves with the same velocity as the first ball.
A cart rams a similar cart and latches onto it with a loud clank.
A cart rams another with a compressed spring, which is released, pushing them apart.

Answer 16

I put B.

Answer 17

You're exactly right. If the velocity of the second pool ball was any less, it wouldn't be perfectly elastic, but since the kinetic energy was 100% conserved (the mass and velocity are the same), it's as perfectly elastic as you can get.

Answer 18

okay thanks Chrismoon!