Example 1

The weight of a body when totally immersed in liquid is 4.2N. if the weight of the liquid displaced is 2.5N, find the weight of the body in the air.

Solution;
Data;
Apparent weight (W2) = 4.2N Weight of liquid displaced (u) = 2.5N Weight of body in air=?
Formular;
U = W1 –W2
W1= 4.2 +2.5 = 6.7N
Weight of body in air is 6.7N


Example 2

Weight of a body in air = 10.0N
Weight of a body when immersed in water = 9.2N find the upthrust. 

Solution:
Data given
Weight of a body in air (W1)= 10.0N
Weight of a body when in water (W2) = 9.2N
Formula
Upthrust = Loss of weight in water = W1-W2 = 10.0N – 9.2N
= 0.8N
The upthrust is 0.8N


Example 3

A piece of glass weigh 1.2N in air and 0.7N when completely immersed water. Calculate its:
1. Relative density
2. Density of a glass

soln
Given that density of water = 1000 kg/cm3 And acceleration due to gravity = 10N/kg Solution
Weight of the glass in air (W1) = 1.2N Weight of the glass in water (W2) = 0.7N
R.D = W1/W1 – W2
1.2N/(1.2 – 0.7)
1.2/0.5
R.D = 2.4
R.D = Density of glass/Density of water
Density of a glass = R.D x Density of water
= 2.4 x 1000 kg/cm
= 2400 kg/m3
NB: Relative density has no SI unit