A person having mass 60kg is standing on a stationary raft in a river. The mass of raft is 40kg. The distance between person and bank is 30m . The person niw starts running towards the bank with velocity of 10mpersec. How far will the person be from the bank after one second.

Dear Student
When the man starts running with velocity 10 m/s towards the bank, the raft will move away from the bank at velocity, say, u. Such that,

M(10) + mu = 0 [by law of conservation of momentum]

=> (60)(10) + (40)u = 0

=> u = -15 m/s [opposite to the direction of man]

So, the velocity of the man towards the bank w.r.t. the ground will be = 10 – 15 = -5 m/s [away from the bank]

In 1 s he travels 5 m away from the bank. So, after 1 s, he is 30 + 5 = 35 m from the bank.

Regards