Question

8. A boy of mass 45 kg running 6 m/s jumps onto a 30 kg trolley moving in the same direction at 1.5 m/s. Their common velocity will be: А. 4.0 m/s B. 4.2 m/s C. 6.5 m/s D. 8.3 m/s​

Answer 1

SOLUTION

TO CHOOSE THE CORRECT OPTION

A boy of mass 45 kg running 6 m/s jumps onto a 30 kg trolley moving in the same direction at 1.5 m/s. Their common velocity will be:

А. 4.0 m/s

B. 4.2 m/s

C. 6.5 m/s

D. 8.3 m/s

EVALUATION

Here it is given that a boy of mass 45 kg running 6 m/s jumps onto a 30 kg trolley moving in the same direction at 1.5 m/s

So by the given

M = Mass of the boy = 45 kg

V = Velocity of the boy = 6 m/s

m = Mass of the trolley = 30 kg

v = Velocity of the trolley = 1.5m/s

v' = Their common velocity

By the principle of conservation of momentum

$\sf MV + mv = ( M + m)v'$

$\sf \implies \: (45 \times 6) + (30 \times 1.5) = ( 45 + 30)v'$

$\sf \implies \: 270+ 45 = 75v'$

$\sf \implies \: 75v' = 315$

$\sf \implies \: v' = 4.2$

Their common velocity = 4.2 m/s

FINAL ANSWER

Hence the correct option is B. 4.2 m/s

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