Find Velocity After Glancing Collision: Antother Collision

[suspenc3]

Antother Collision!

A billiard ball moving with a speed of v = 2.2m/s strikes an identical stationary ball a glancing blow. After the collision, one ball is found to be moving at a speed of v_2 = 1.1m/s in a direction making a \theta = 60^o angle with the original line of motion. Find the velocity of the other ball?

I don't really know where to start...Maybe conserving momentum?

 

[suspenc3]

Would I just do this:

1/2m_1v_1_i^2 +1/2m_2v_2_i^2 = 2(1/2m_1v_1_f^2) + 1/2m_2v_2_f^2

since all of the masses are the same they cancel out and since the second ball is stationary..it is 0

v_1_i^2 = 2v_1_f^2 + 2v_2_f^2
1/2(2.2)^2 = 2sin \theta(1.1)^2 + 2v_2_f^2
v_2_f = 1.53m/s

 

[Astronuc]

Would I just do this:
1/2m_1v_1_i^2 +1/2m_2v_2_i^2 = 2(1/2m_1v_1_f^2) + 1/2m_2v_2_f^2

Why is the kinetic energy term of m₁ doubled on the right hand side?

In an elastic collision, kinetic energy and momentum are conserved. Momentum is conserved in the x and y directions.