What Happens to Sphere Velocities After an Elastic Collision?

[Manh]

Homework Statement

Two solid spheres hung by thin threads from a horizontal support (Figure 1) are initially in contact with each other. Sphere 1 has inertia m1 = 0.040 kg , and sphere 2 has inertia m2 = 0.10 kg. When pulled to the left and released, sphere 1 collides elastically with sphere 2. At the instant just before the collision takes place, sphere 1 has kinetic energy K1 = 0.086 J .
A. What is the speed of sphere 1 after the collision?
B. What is the speed of sphere 2 after the collision?

Homework Equations

K = 1/2 mv^2
p = mv

The Attempt at a Solution

I found v1i = 2.07 m/s
Should I consider of using these equations?
Kinetic:
1/2 m1*v1i^2 + 1/2 m2*v2i^2 = 1/2 m1*v1f^2 + 1/2 m2*v2f^2
Momentum:
m1*v1i + m2i*v2i = m1*v1f + m2*v2f

 

[andrewkirk]

Yes. You have two unknowns - the velocities of the two spheres after the collision - and two equations (one for momentum and one for KE), so you can solve the system and find both values.