Question

A wooden block floats in glycerine in such a way that it's 2/5 volume remains above surface. If relative density of wood is 0•78. Calculate the relative density of glycerine.

Answer 1

Relative density of wood is 0.78. This means, the density of wood relative to an equal volume of water is 0.78.
Water is 1 gram per cc. so if 2/5 of a wood floats in glycerine, then the weight of 5/5 of glycerine is 5/3 x mass of wood.
Take the density of wood as 0.78 g/cc.
Hence since 2/5 of the wood is floating above glycerine, the density of glycerine is 0.78 x 5/3 = 1.3 g/cc.
Thus the RD of glycerine is 1.3.