Question

A raft of wood (density $600kg/m^3$) of mass $120kg$ floats in water. The weight that can be put on the raft to make it just sink is :

• A. $120kg$
• B. $200kg$
• C. $40kg$
• D. $80kg$

Answer 1

The correct option is D $80kg$

Density of raft = $600kg/m^3$
mass of raft$=120kg$
Volume of wood $=\frac{120}{600}{m}^3$ $=\frac{1}{5}{m}^3$
So, Total upthrust from water if the raft is fully dipped in water $\frac{1}{5}\times 1000kg/m^3$ $=200$ kg
So, the raft will sink if total upthrust = total downward force,
So, weight that can be $(200-120)kg$$=80$ kg