A boy of mass 50 kg running at 5 m/s jumps on to a 20 kg trolley travelling in the same direction at 1.5 m/s. What is their common velocity?
Using conservation of momentum
MV + mv = (M + m) v'
Where:
M - Mass of the boy - 50kg
m - Mass of the trolley - 20kg
V- Velocity of the boy - 5m/s
v - Velocity of the trolley - 1.5m/s
v' - common velocity - x
(50+20) x = (50x5 +20x1.5)
x= 4m/s.
Hence, the common velocity is 4m/s.