NEET 2024 — Physics solution

NEET2024Physics

A thin flat circular disc of radius 4.5 cm is placed gently over the surface of water. If surface tension of water is $0.07$ Nm $^{- 1}$ , then the excess force required to take it away from the surface is:

A
1.98 mN
B
99 N
C
19.8 mN
D
198 N

Solution

Surface tension acts along the circumference: $F = T \times (2 π R)$ .

$F = 0.07 \times 2 π \times 4.5 \times 1 0^{- 2} = 0.07 \times 0.2827 \approx 0.0198$ N $= 19.8$ mN.

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