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.


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