Question

An object weights $500\,g$ in air. This object is then fully immersed in water. State whether it will weigh more in water or less in water. Give reason for your answer.

Answer 1

Hint: This question is based upon the principle of buoyant force which is sometimes also known as buoyancy. We will compare this buoyant force with the force of gravity and then by using Archimedes’ principle, we will conclude whether it will weigh more or less.

Complete answer:
Let us first understand the concept of Archimedes principle which states that “When a body is partially or fully immersed in fluid it’s acted by an upward force which is equal to weight of the fluid displaced by the body” and this force is known as buoyant force.It acts in the upward direction which is the direction just opposite to that of force of gravity.

Now, when the object of weight $500\,g$ is immersed in water it experiences a buoyant force in the upward direction. An object also displaces some fluid whose weight is equal to this buoyant force so while remaining in fluid the apparent weight of the object decreases due to this buoyant force.

Hence, when an object is fully immersed in water its weight gets decreased due to the force acting on it in an upward direction which is called buoyant force.

Note:Remember, buoyant force is mainly depends upon the density of the fluid and the volume of fluid which an object displaces when immersed in a fluid and the magnitude of buoyant force is given as ${F_b} = - \rho gV$ , negative sign indicates that its direction is opposite to that of force due to gravity.