# Elastic vs. Completely Elastic?

1. Nov 30, 2013

### nx01

1. The problem statement, all variables and given/known data

A 2.4kg ball falling vertically hits the floor with a speed of 2.5m/s and rebounds with a speed of 1.5m/s. The impact or "collision" described in this problem is:

a. completely elastic
b. completely inelastic
c. elastic
d. inelastic

2. The attempt at a solution

As I understand it, the collision in this problem is "inelastic". However, the answer choices make a distinction between "completely elastic" and "elastic" collisions. Since there are no elastic collisions on the macroscopic scale, this cannot be a "completely elastic" collision. Yet, since some macroscopic collisions are approximated as elastic collisions, this might count as an "elastic" collision.

Is the distinction between elastic and completely elastic collisions a legitimate one, or is it there just to throw me off? How would you answer this question?

Thanks!

2. Nov 30, 2013

### vela

Staff Emeritus
I think it's there just to throw you off. A collision is either elastic or not. On the other hand, an inelastic collision isn't necessarily completely inelastic, so it makes sense to make a distinction.

3. Nov 30, 2013

Thank you!