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A thin metal disc of radius r floats on ...

A thin metal disc of radius `r` floats on water surface and bends the surface downwards along the perimeter making an angle `theta` with vertical edge of the disc. If the disc displaces a weight of water `W` and surface tension of water is `T`, then the weight of metal disc is :

A

`2pirT+W`

B

`2pirTcos theta-W`

C

`2pirTcos theta+W`

D

`W-2pirTcos theta`

Text Solution

Verified by Experts

The correct Answer is:
C
Weight of metal disc = total upward force
= upthrust force + force due to surface tension
= weight of displaced water `+ T cos theta (2pir)`
`W+2pirTcos theta`
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