A boat of mass 40 kg is floating on water. A boy of mass 10 kg on the boat moves by 8m on boat towards the shore. The distance by which the boat moves away from the shore is ______m.

As there is no external force acting on the boy + boat system.

the position of the center of mass will not change

If the boat displaces by S, the net displacement of the boy w.r.t ground is L-S

$\Rightarrow \mathrm{m}(\mathrm{L}-\mathrm{S})=\mathrm{MS}$

$\Rightarrow \mathrm{S}=\frac{\mathrm{mL}}{\mathrm{M}+\mathrm{m}}=\frac{10\times 8}{50}=1.6\mathrm{m}$