Question

A piece of aluminum is suspended from a string and then completely immersed in a container of water. The mass of the aluminum is 1 kilogram and its density is 2.7 X 103 kg/m3 . Calculate the tension in the string before and after the aluminum is immersed in water.

Answer 1

The tension in the string before:

$$T=mg=9.8\text{ N}.$$

The tension in the string after submersion:

$$T=mg-\rho_wg\frac{m}{\rho}=6.2\text{ N}.$$