Question

A ball of mass 0.50 kg moving at a speed of 5.0 m/s collides with another ball of mass 1.0 kg. After the collision the balls stick together and remain motionless. What was the velocity of the 1.0 kg block before the collision?

Answer 1

It is given that:
Speed of the ball, v₁ = 5.0 m/s
Mass of the ball, m₁ = 0.5 kg
Mass of another ball, m₂ = 1 kg
Let the velocity of this ball be v₂ m/s.

On applying the law of conservation of momentum, we get:

$$\begin{gathered} m_1{v}_1+m_2{v}_2=0 \\ 0.5\times 5+1\times v_2=0 \\ \Rightarrow v_2=-2.5\mathrm{m}/\mathrm{s} \end{gathered}$$
Hence, the velocity of second ball is 2.5 m/s, opposite to the direction of motion of the first ball.