Hi, heres 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.