# Conservation of Momentum and Energy

**1. The problem statement, all variables and given/known data**

This is the question show that when one of the steel balls, suspended by strings next to

each other (as in a newton’s cradle), is pulled to the left and released, only a single ball recoils to

the right under ideal elastic-collision conditions. Assume that each ball has a mass m

, and that the ball coming in from the left strikes the other balls with a speed v0. Now, consider the hypothetical case where one ball comes from the left but two balls recoil to the right.

Determine the speed the two recoiling balls must have in order to satisfy

(a)(3 marks) momentum conservation, and

(b)(3 marks) energy conservation.

**2. Relevant equations**

momentum p =mv

energy k = .5 mv^2

**3. The attempt at a solution**

I assumed in both cases I would put p1=p2, and k1=k2, where the masses of the two recoiling balls, p2 and k2, will be 2m, and so find v in that way but that doesn’t work. don’t know what else to try.

http://ift.tt/NOqJxo

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