Question

8. All KE is lost when:
(a) two bodies of equal mass collide,
(b) two bodies of opposite initial velocity collide,
(c) two bodies of equal mass and opposite initial velocity collide,
(d) never.

Answer 1

Yes. Of course.

Answer 2

I think no choice is correct.

Answer 3

8. All KE is lost when:
(a) two bodies of equal mass collide, : NO: BILLARD BALLS
(b) two bodies of opposite initial velocity collide, NO: BILLARD BALLS BOUNCE OFF.
(c) two bodies of equal mass and opposite initial velocity collide, NO: BILLARD BALLS BOUNCE OFF.
(d) never. NO: ELASTIC COLLISIONS EXIST.

Answer 4

Sorry, I wrote in caps to make it look visible.

Answer 5

If you don't mind me asking, which grade/univeristy level are you?

Answer 6

You're looking at an isolated scenario. Answering T/F questions require generalizations. You're looking at inelastic collisions.

Answer 7

No, I found a counterexample.

Answer 8

No, I'm not against you! I'm trying to find the right answer :P

Answer 9

@amistre64 @beccaboo333 @berrypicking @crazyblue @iPwnBunnies @iceicebaby

Answer 10

@zepdrix

Answer 11

@robtobey @Luigi0210

Answer 12

Well. I think D could be possible. Elastic collisions are when no Kinetic Energy is lost, and the question is asking when ALL Kinetic Energy is lost.

Answer 13

Yeah this is a poor question. Doesn't ask if it's an elastic or inelastic collision.

Answer 14

I agree, poorly worded. I would go with D: never. It's really not the case that KE cannot be completely lost in a collision. But, given all the collision scenarios you can think of, it would be mostly the case.

For D to be true, you must agree that there does not exist any purely inelastic collisions. That seems much better than the rest. Especially because, considering just momentum transfer, there is no such thing as purely elastic or purely inelastic, right? Just situations so similar so that ideal approximations are still accurate?