question_answer

A solid body floats on mercury with a part of its volume below the surface. Will the fractional volume of the body immersed in mercury increase or decrease, if a layer of water poured on the top of mercury covers the body completely?

Answer:

                In the first case, the weight of the body is balanced by the weight of mercury displaced. But when water is poured to cover the body completely, the weight of (mercury + water) displaced by the body is equal to the weight of the body. The weight of mercury displaced is now less than that in the first case. So the fractional volume of the body inside the mercury will decrease.