A person of mass 60 kg is standing on a raft of mass 40 kg in a lake. The distance of the person from the bank is 30 m. If the person starts running towards the bank with velocity 15 m/s, then what will his distance be from the bank after two second

Options

A. 26 m
B. 18 m
C. 21m
D. 12m

Answer

B

Explanation

When a person starts running towards the bank the sytem moves backwards
Here velocity of person w.r.t raft `vec(v ) _(pR) = 15 hat(I ) m //s`
Let the direction of running be x- axis
Since no external force is acting on this system as per the law of conservation of momentum
[Final momentum of the system ]
`vec(V ) _(RB ) = 9 hat(i ) m//s`
Therefore from eq. (i ) `vec(V )_(PB) = (15-9hat(i)) = 6hat(i) m//s`
Thus the person travels an effective distance of 6 min is towards the bank so after 1 s his distance from the bank is 30 -12 = 18 m