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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?

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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?

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Mass of the boy, m1= 50 kg

Speed of boy, u1 = 5 m/s

Mass of trolley m2 = 20 kg

Speed of trolley u2 = 1.5 m/s

Combined mass of boy and trolley, m = 20 + 50 = 70 kg

Combined velocity v

Acc. to the law of conservation of momentum

m1u1 + m2u2 = mv

50 x 5 + 20 x 1.5 = 70 x v

v = \(\frac{250 + 30}{70}\) = 4 m/s

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