Laws Of Motion Question 178

Question: A man weighing 80 kg is standing in a trolley weighing 320 kg. The trolley is resting on frictionless horizontal rails. If the man starts walking on the trolley with a speed of 1 m / s, then after 4 sec his displacement relative to the ground will be[CPMT 1988, 89, 2002]

Options:

A) 5 m

B) 4.8 m

C) 3.2 m

D) 3.0 m

Show Answer

Answer:

Correct Answer: C

Solution:

If the man starts walking on the trolley in the forward direction then whole system will move in backward direction with same momentum. Momentum of man in forward direction = Momentum of system (man + trolley) in backward direction therefore 80×1=(80+320)×v therefore v=0.2 m/s So the velocity of man w.r.t. ground 1.00.2=0.8 m/s

Displacement of man w.r.t. ground =0.8×4=3.2 m



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