1. ## Elastic collision

Hi I'm stuck on a problem with a elastic collision.

wagon1 has the mass 1 kg and the velocity 3 m/s, collides with wagon which has the mass 2 kg and is standing still, what are the wagon's velocity after the collision?

2. Momentum is conserved, so $m_1v_1+m_2v_2=m_1v_{init}$, where $m_1$ and $m_2$ are the masses, $v_{init}$ is the initial velocity, and $v_1$ and $v_2$ are the final velocities. Since the collision is elastic, kinetic energy is also conserved, so $\frac{1}{2}m_1v_1^2+\frac{1}{2}m_2v_2^2=\frac{1}{2 }m_1v_{init}^2$.

I think you can solve it from there. You should get $v_1=-1$ and $v_2=2$, so wagon 1 bounces and is coming back the other direction at 1 m/s, and wagon 2 moves at 2 m/s.

- Hollywood