# Collision of 2 balls in air

1. May 12, 2012

### rh0mbus

1. The problem statement, all variables and given/known data
Two elastic balls of mass m1 = 0.3kg and m2 = 0.2kg are hanging on a thin rope so that their centre of gravity is on the same height. ball 1 goes out of balance raising it up to h0 = 0.05m
Then letting it go hitting ball 2. Calculate the maximum height of both balls reaching after the collision.

m1 = 0.3kg
m2 = 0.2kg
h0 = 0.05m
g = 10m/s2
and since m2 is not moving it's V2 = 0m/s

h1 = ?
h2 = ?

2. Relevant equations
I'm not 100% sure,
but I do know I am supposed to use the elastic collision equation:
m1*V1+m2*V2 = m1*V1'+m2*V2' since V2 = 0m/s it's:
m1*V1 = m1*V1'+m2*V2'

And I'm guessing kinetic energy:
ΔEk = 4 * m1*m2/(m1+m2)2 * Ek1
Ek1 = 1/2*m1*V12

3. The attempt at a solution
First I made a drawing of it to understand it better.
I just don't see how am I supposed to collide those 2 equations and then the height.
And what am i supposed to do with g = 10m/s2 ??

Last edited: May 12, 2012
2. May 12, 2012

### vanihba

By raising the ball to a ht. of ho, you give it a potential energy change of mg(ho), which will be converted to Kinetic energy when the ball comes down
mgho = 1/2m(v1^2), thus u get v1.

Find final velocities. use potential energy again after that.

3. May 13, 2012

### rh0mbus

I've managed to finish the problem after your help. Thank you!

h1 = 0.0125m
h2 = 0.072m