Question

A man weighing 80 kg is standing at the centre of a flatboat and he is 20 m from the shore. He walks 8 m on the boat towards the shore and then halts. The boat weight 200 kg. How far is he from the shore at the end of this time?

Answer 1

The center of mass of the system has zero net displacement, since the boat and the boy move in opposite directions.

Let the boat moves a distance x from the shore.So, the boy moves a distance (x-8).

$\therefore M_1{X}_1+M_2{X}_2=0$

$\therefore \left(200\right)x+\left(80\right)(x-8)=0$

$\Rightarrow x=2.3m$

So, displacement of the boy towards the shore = (8-2.3)=5.7 m

So, the boy is (20-5.7 = 14.3m) far from the shore at the end of this time.