Question

State whether the weight of an iron sinker with cork combined in water will be more or less than that of the iron sinker alone in the water.
A. Less
B. More
C. Same
D. None of the above

Answer 1

Archimedes principle is the greatest invention, which helps to solve the problems in fluid mechanics. It deals with the weight of the fluid displaced when an object is immersed inside the fluid and a new term called buoyancy force came into existence after that. Based on this concept only we solve this problem.

Complete step-by-step solution
Usually, when we immerse an object in the water then that object will displace some volume of the water and that will float on the water. That is floating in the sense it is in equilibrium which means forces are balanced. Weight will be always acting downwards but the object is not moving down it is floating which means there must be a force acting upwards which balances this weight and that force is called buoyancy force.
According to the Archimedes Principle, the weight of the fluid displaced will be equal to the buoyancy force acting on the object.
According to the question, when the iron sinker combined with the cork is immersed in the water completely, the buoyancy force acting on the cork will be more than its weight, which means the upward force is more than the downward force. When we remove the cork and immerse only the iron sinker there is no previous upward dominating force and weight will be more this time.
Hence as net upward force will be present on the cork, the iron sinker combined with cork weighs less than the iron sinker alone.
Hence option A is correct.

Note: There is a particular condition for floating. If the density of the body is less than the density of fluid then the body floats and if the density of the body is more than the density of fluid then the body will sink. Iron is denser than water so it will try to sink and cork is less dense than water, so it will try to float.