Question

A spherical object of density $\rho$ is immersed in a fluid of density $\sigma$. The object will move :

• A. Downwards if $\rho >\sigma$
• B. Downwards if $\sigma <\rho$
• C. Upwards if $\sigma <\rho$
• D. Upwards if $\rho >\sigma$

Answer 1

Answer: (A), (C)

Downwards if $\rho >\sigma$
Upwards if $\sigma <\rho$

The object, when completely immersed in fluid, experience buoyancy force ($V\sigma g$) in upward direction and gravitational force ($V\rho g$) in the downward direction.

When the density of object is higher than that of fluid ($\rho >\sigma$), gravitational force is more than the buoyancy force and the object moves downwards.

While, when the density of object is lesser than that of fluid ($\sigma >\rho$), gravitational force is less than the buoyancy force and the object moves upwards.