# Collision problems

1. Nov 7, 2004

### jenavira

Collision problem

After a completely inelastic collision, two objects of the same mass and same initial speed are found to move away together at half their initial speed. Find the angle between the initial velocities of the objects.

I've got the equations
(2mv)cos theta1 = 2m.5v cos theta2
&
mv sin theta1 = 2m.5v sin theta2

But I'm not sure where to go from there. (Actually, I'm not sure how to get a numerical answer out of something I haven't been given any numbers to put into, so there's probably a conceptual thing I'm missing here...)

Last edited: Nov 7, 2004
2. Nov 7, 2004

### Andrew Mason

Try using:

$$mvsin\theta + mvsin\alpha = 0$$

where $\theta$ and $\alpha$ are the respective angles of the initial velocities of the respective masses relative to the final velocity of the two masses together. This tells you that the angles are equal (after all, why should they be different?).

The rest should be obvious.

AM