Question

Assertion: To float, a body must displace liquid whose weight is greater than the actual weight of the body.
Reason: The body will experience no net downward force, in the case of floating.
A. If both assertion and reason are correct and Reason is the correct explanation for Assertion.
B. If both assertion and reason are correct and Reason is not the correct explanation for Assertion.
C. Assertion is correct but the reason is incorrect.
D. Both Assertion and Reason are incorrect.

Answer 1

We should recall the principle of Archimedes principle to know the concept behind a body immersed in a liquid. The body immersed in liquid experiences an upward force as well as a downward force.

Complete step by step solution:
Let us first examine the situation in the given problem.
A body is immersed in a liquid and it is floating. For a body immersed in a liquid, it experiences an upward force called upthrust which is equal to the weight of the liquid displaced by the body in liquid and also the body experiences a downward force due to the weight of the body itself.
Now for a body to float in the liquid the upthrust should be greater than the weight of the body, that is the upward force should be greater than the downward force. Now we know that the upthrust is the upward force which is equal to the weight of the liquid displaced. So the weight of the displaced liquid will be more than the actual weight of the body which causes the downward force in this case (floating).
Therefore the assertion in the question is correct. Now let us look at the reason given
The reason says that the body will experience no net downward force which is true because the body is floating and the upward force is playing a dominant role. But the reason is just a general statement without any further explanation that the downward force is balanced by the upward force and thus the body has no net downward force.
Thus both the assertion and reason are correct but the reason is not the correct explanation for Assertion.
Hence option (B) is correct.

Note: If the body is sinking, the net downward force is greater than the upward force or the thrust provided by the buoyant force. In that case, the weight of the displaced liquid by the body is equal to the buoyant force.