Question

A man of mass 60 kg is standing on a boat of mass 140 kg. which is at rest in still water. the man is initially at 20 m from the shore. he starts walking on the boat for 4 s with constant speed 105 m/s towards the shore. the final distance of the man from the shore is (1) 15.8 m (2) 4.2 m (3) 12.6 m (4) 14.1 m

Answer 1

The  man moves with a speed of 1.5 m/sec for 4 sec . So distance travelled by the man during this time period is 6 m. Let us assume the shore is to our left , when the moves towards the shore there will be a relative displacement of boat towards right . So the relative displacement of boat is = md/(M+m) , where m is mass of man ,and d is the distance he walks towards the shore and M is the mass of boat .after substituting the values given we get the relative displacement to be1.8m.so the total distance from the shore is = initial distance from the shore – distance walked by the man + relative displacement of boat = 20-6+1.8=15.8m

Answer 2

Answer:

15.8

Explanation:

S=d/t

1.5=d/4

d=6m

By com formula

md+MD/m+d

60*6+140*0/200

Total distance from shore=20+1.8-6 =15.8 m