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A wooden block is floating in a water ta...

A wooden block is floating in a water tank. The block is pressed to its bottom. During the process, work done is equal to :

A

work done against upthrust exerted by the water

B

work done against upthrust plus loss of gravitational potential energy of the block

C

work done against upthrust minus loss of gravitational potential energy of the block

D

None of these

Text Solution

Verified by Experts

The correct Answer is:
C
(c ) Initialy the wooden block floats when partially in mersed in water. Initially, upthrust exerted by water is exactly equal to the weight of the block. But when it is pressed down then more water is displaced. Hecne up thrust exerted by water increases. The force required to press down the block is equal to F = upthrust -mg. Hence, work done by the force F will be equal to work against (upthurst -mg) it means work done by the external force is equal to (work done against upthrust loss of gravitational potential energy of the block).
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