(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A 90-g ball moving at 100 cm/s collides head-on with a stationary 10-g ball. Determine the speed of each after impact if (a) they stick together, (b) the collision is perfectly elastic.

2. Relevant equations

p=mv

3. The attempt at a solution

I already solved A, but I don't know how to do B. So far, I've gotten:

p=mv

= 90(100)

= 9000 g.cm/s

p=mv

= 10 (0)

= 0

so...

p1+p2=p3

m1 v1 + m2 v2 = (m1 +m2)v

90(100) + 0 = 100v

v= 90 cm/s

I don't understand how the answer can be 80 cm/s when they perfectly elastic. Shouldn't it be 90 cm/s?

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# Homework Help: Elastic Collision of a 90kg ball

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