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

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

(a)5 m

(b) 4.8 m

(c) 3.2 m

(d) 3.0 m

Click to See Answer :
Ans: (c)
Sol: On applying conservation of linear momentum ,

80 x 1 = (80 + 320)v

v = 0.2 m/s

Velocity of man with respect ot ground = 1.0 – 0.2 = 0.8 m/s

Displacement of man relative to the ground

= 0.8 × 4 = 3.2 m