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\times 1=(80+320)\times v $ therefore $ v=0.2\ m/s $ So the velocity of man w.r.t. ground $ 1.0-0.2=0.8\ m/s $
$ \therefore $ Displacement of man w.r.t. ground $ =0.8\times 4=3.2\ m $
