Question:
A ball of mass $0.50 \mathrm{~kg}$ moving at a speed of $5.0 \mathrm{~m} / \mathrm{s}$ collides with another ball of mass $1.0 \mathrm{~kg}$. After the collision the balls stick together and remain motionless. What was the velocity of the $1.0 \mathrm{~kg}$ block before the collision?
Solution:
Use C.O.L.M
$m_{1}=0.5, v_{1}=\frac{5 m}{s}, m_{2}=1, v_{2}=?$
$0.5 \times 5+1 \times v_{2}=0$
$v_{2}=-2.5 \mathrm{~m} / \mathrm{s}$