Question

A body weighs w in air and it loses its weight by 25% in water. The relative density of the body is

Answer 1

Given,
weight in air = (10 + 0.1) N
weight in water = (5 ± 0.1) N
∴ Loss of weight in water = weight in air - weight in water
= (10 ± 0.1) N - (5 ± 0.1) N
= (10 - 5) ± (0.1 + 0.1) [ in case of error , you should always take addition ]
= (5 ± 0.2) N

Now, relative density = weight in air /loss of weight in water
= (10 ± 0.1)N/(5 ± 0.2)N
= (10/5) ± [0.1/10 + 0.2/5] × 100
[ Actually, % error = [∆w/W + ∆w'/W']×100 , here w is weight in air and w' is loss of weight in water ]
= 2 ± [1 + 4]%
= 2 ± 5%
hence, maximum % error = 5%