Wooden plank weighing 8kg floats in water with two-fifth of its volume floating in water. Find the maximum weight that can be placed over the plank so that it may float completely submerged.
Let V be the volume of the plank.
Given that two-fifth volume of plank is submerged in water.
Therefore by law of floatation the weight of wooden plank is equal to the weight of
volume of water.
of water = 8 kg
Weight of V volume of water=20kg.
Therefore when wooden plank is fully submerged in water, it displaces 20 kg of water.
Hence a 20 kg weight can be made to float over the water.
Thus additional weight that can be put over the plank is (20 – 8)kg = 12 kg.