Question

A man of mass 60 kg is standing on a raft of mass 500 kg that is still. With what speed should he run
so that the raft starts moving with a speed of 1.8 km/hr ?

Answer 1

Answer:

Complete step by step answer:

Speed of the man walking on the boat is, v=1.5ms−1v=1.5ms−1

Total time he was walking on the boat. t=4st=4s

Now, the distance covered by the man in the boat is,

s=vts=1.5ms−1×4ss=6ms=vts=1.5ms−1×4ss=6m

The man will walk forward on the boat by 6 m. Now, the boat will also displace in the opposite direction to make the position of the centre of mass of the whole system undisturbed.

Suppose, the velocity of the boat in the opposite direction is V and the distance it goes backwards is x.

Now, according to conservation of momentum law, the initial momentum of the system is equal to the final momentum of the system.

(140+60)×V=60×1.5V=60×1.5200V=0.45ms−1(140+60)×V=60×1.5V=60×1.5200V=0.45ms−1

So, velocity of the boat will be V=0.45ms−1V=0.45ms−1

So, the displacement of the boat in the backward direction is given by,

S=VtS=0.45ms

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