Question

A raft of wood (density=600kg//m^(3)) of mass 120 kg floats in water. How much weight can be put on the raft to make it just sink?

Answer 1

Downward acting force will be Mg that is mass of raft and gravity acting on it.

Upward acting force is buoyancy force of water that is V¶g that is volume of raft*density of water*gravity.

Now take the extra mass to be added as x,

Mg = V¶g

M = V¶

120 + x = (120/600) * 1000

Since density of water is 1000kg/m³

120 + x = 0.2*1000

120 + x = 200

x = 80

Therefore, to make the raft just sink the mass added should be near to 80 kg