4. Assertion : To float, a body must displace liquid whose weight is greater than the actual weight of the body. Reason : The body will experiences no net downward force, in the case of floating.

(a)       If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b)       If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c)        If assertion is true but reason is false.

(d)       If the assertion and reason both are false.

(e)       If assertion is false but reason is true.

Explanation-(c) Net force = actual weight – upthrust force

= Actual weight – Weight of liquid displaced.

The body will rise above the surface of liquid to such an extent that the weight of the liquid displaced by the immersed part of the body (i.e. upward thrust) becomes equal to the weight of the body. Thus the body will float when upward thrust is more than its actual weight. In this special case the density of solid body is less than the density of liquid.

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