A ball of mass m1 is moving with a velocity v0 along the x axis and collides with a ball of mass m2 which is at rest. The balls have an elastic...

A ball of mass m1 is moving with a velocity v0 along the x axis and collides with a ball of mass m2 which is at rest. The balls have an elastic collision. After the collision, ball m1 is moving with a velocity v1 at an angle theta1 with the x axis and ball m2 is moving with a velocity v2 at an angle theta2 with the x axis as shown in the figure. Let m1=2.0kg, v0=5.0m/s, and m2=8.0kg. The momentum, p2, of mass 2 after the collision=12.028kg m/s and makes an angle theta2=20 degrees above the x axis. What is the magnitude of the momentum, p1, after the collision? The answer is 6.59 kg/,^3, but I don't know how to prove this. Please see the attached picture for an illustration of the problem.