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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 of the disc. If the disc dispplaces a weight of water `W` and surface tension of water is `T`, then the weight of metal disc is

A

`2pirT+W`

B

`2pirTcostheta-W`

C

`2pirTcostheta+W`

D

`W-2pirTcostheta`

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 `+Tcostheta(2pir)`
`=W+2pirTcostheta`
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