Question

A stationary 3-kg hard steel ball is hit head-on by a 1-kg hard steel ball moving to the right at 4 m/s. After the collision, the 3-kg ball moves to the right at 2 m/s. What is the velocity (speed and direction) of the 1-kg ball after the collision?

Answer 1

From conservation of momentum we have that:

$\begin{gathered} 1(4)+3(0)=1v+3(2) \\ 4=v+6 \\ v=4-6 \\ v=-2 \end{gathered}$

Therefore the velocity of the 1 kg ball after the collision is 2 m/s to the left.