Question
Question: A thin metal disc of radius r floats on water surface and bends the surface downwards along the peri...
A thin metal disc of radius r floats on water surface and bends the surface downwards along the perimeter making an angle θ with vertical edge of 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
2πrT + W
B
2πrTcosθ – W
C
2πrTcosθ + W
D
W – 2πrTcosθ
Answer
2πrTcosθ + W
Explanation
Solution
Weight of metal disc = total upward force
= upthrust force + force due to surface tension
= weight of displaced water + T cos θ (2π r)
= W + 2π rT cos θ