Elastic collision between two billiard balls

[phyme814]

Homework Statement

Two balls collide on a frictionless surface. Mass m1 = .4 kg and Mass m2 = .3 kg . The initial velocity of m1 is 3 m/s. While m2 is at rest. After the collision the velocity of m1 is 1.5 m/s, θ1 above the horizontal. While m2 gains an unknown velocity of v2f, θ2 below the horizontal.
Find v2f, θ1, and θ2

Homework Equations

Conservation of kinetic energy
Conservation of momentum

The Attempt at a Solution

I can find v2f, but I am having trouble with finding the angles.

 

[Doc Al]

I can find v2f, but I am having trouble with finding the angles.

Show what you did.

 

[Doc Al]

I presume you used conservation of energy to solve for v2f. Now use conservation of momentum to solve for the angles. (You'll get two equations and two unknowns.)

 

[phyme814]

Yepp I used conservation of kinetic energy.
I was using the conservation of momentum equation for the unknowns of the angles but I was running into trouble because I would get sinθ1 and sinθ2 in one equation and cosθ1 and cosθ2 in the other equation.

 

[Doc Al]

but I was running into trouble because I would get sinθ1 and sinθ2 in one equation and cosθ1 and cosθ2 in the other equation.

Sine and cosine can be related by a trig identity.