# Elastic collision in a pendulum

1. Apr 24, 2008

### Jenez

Hello people. New here and i've got a problem here which i would appreciate some help with.

Situation :
A ball of mass 300g is attached to a massless string of 0.2m suspended at a 90 degree angle to another ball of mass 500g held by a massless string at length 0.2m.
Imagine the ball A (0.3kg) is positioned next to ball B, which are equal except for masses. Ball A is moved in a quarter of a circle motion up 0.2m, keeping it's string straight. That is the case we are examening.
The question is, what are the maximum heights ball A and B can attain after ball A is released collides with B?

We assume that this is an insulated system, meaning 100 % conserved energy and momentum.

Through PEi + KEi = PEf + KEf We achieve the velocity 1.98 m/s right before collision with ball B.

The problem arises when the total KE for the system has to be distributed correctly between ball A and B post-collision. I've reached the point where the KEi = Va final + 5/3 Vb final

How do you go about finding either one of the velocities? I know that the V of B will be greater than V of A since B has less than double the mass of A

2. Apr 28, 2008

### Phlogistonian

Use the formulas for an elastic collision.

$$p_{before} = p_{after}$$

$$KE_{before} = KE_{after}$$

That will give you 2 equations with 2 unknowns.