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?

Options

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

Answer

D

Explanation

Volume of raft = `V = (mass)/(density)`
`V= 120/600 = 1/5 m^(3)`
when the raft is totally immersed in water, it displacess `1/5 m^(3)` water, so the upthrust
`=1/5 xx 1000 xx g newton
if `x kg` is the extra weight put on the raft to fully immerse it in water, then
`(x+120)g = 1/5 xx 1000 xx g or = x + 120 = 200`
`x =80 kg`.