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**1. Homework Statement**

A cube of mass m slides without friction at a speed vo. It undergoes a perfectly elastic collision with the bottom tip of a rod length d and mass 2m. The rod is pivoted about a frictionless axle through its center, and initially it hangs straight down and is at rest. What is the cube's velocity- both speed and direction after the collision?

**2. Homework Equations**

Moment of inertia for rod pivoted about center I=(1/12)mr^2

**3. The Attempt at a Solution**

I used conservation of energy

Kcubeinitial = Krotational of rod + Kcubefinal

I replaced angular velocity with v1/.5d

.5mvo^2 = .5mvf^2 + .5(1/12)2md^2 * (v1/.5)^2

Then I used conservation of momentum:

mvo= mvf + 2mv1

But substituting these two equations into each other leads to something I can't solve. Should I try angular momentum?