Elastic Collision, Finding Angles Between Particles

[Kyliticus]

Hi, here's my problem.

A particle of m1 and initial speed v0 strikes a stationary particle of mass m2, and scatters at 30 degrees to its original direction with speed v0/3. Find the angle, in degrees, between the directions of the two particles after the collision.

I found that the velocity of the m2 after the collision to be 2/3v0 due to conservation of energy.

Can anyone give me ideas on how to find the contained angle? Thank you.

 

[nasu]

You need to use conservation of momentum as well. In this case you have a 2D case so write momenta along two axes (x and y) and their conservation for each axis.

How can you find the speed from energy conservation, as long as you don't know the masses?