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## Homework Statement

You slide a 2 kg block on a flat icy surface towards a static block of mass M. Before the collision, the 2 kg mass is moving at 3 m/s. The total kinetic energy is not changed by the collision. After the collision, the 2 kg mass is moving at −1 m/s i.e. opposite to its original direction. Calculate the mass M in kg and the velocity of the mass M after the collision.

## Homework Equations

Eq 1.) 0.5mv

_{1i}

^{2}+0.5Mv

_{2i}

^{2}=0.5mv

_{1f}

^{2}+0.5Mv

_{2f}

^{2}

Eq 2.) mv

_{1i}+Mv

_{2i}=mv

_{1f}+Mv

_{2f}

## The Attempt at a Solution

I got v

_{2f}=2 m/s and M=4 kg. I solved for M for the second equation and substituted that in into the first equation.