A rectangular blade of negligible weight floats on a water surface of surface tension $\frac{1}{7} \times 10^{- 1} N / m$ . Its internal and external perimeter is 6a and 8a respectively then minimum force to lift up blade from water surface is $x \times 10^{- 2}$ N, then $x$ is (Take a = 10 cm )

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Solution

The correct option is A 2
Total perimeter $= 14 a$
Force needed to lift blade up
$=$ Surface tension $\times$ Perimeter
$= T \times 14 a$
$= \frac{1}{7} \times 10^{- 1} \times 14 \times 10 \times 10^{- 2} = 2 \times 10^{- 2} N$

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A rectangular blade of negligible weight floats on a water surface of surface tension $\frac{1}{7} \times 10^{- 1} N / m$ . If the minimum force to lift up blade from water surface is $2 \times 10^{- 2} N$ , then find the internal perimeter of blade. [Take a = 10 cm]

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A rectangular blade of negligible weight floats on a water surface of surface tension 17×10−1N/m. Its internal and external perimeter is 6a and 8a respectively then minimum force to lift up blade from water surface is x×10−2 N, then x is (Take a = 10 cm )

The correct option is A 2Total perimeter =14a Force needed to lift blade up = Surface tension × Perimeter =T×14a =17×10−1×14×10×10−2=2×10−2 N

A rectangular blade of negligible weight floats on a water surface of surface tension $\frac{1}{7} \times 10^{- 1} N / m$ . Its internal and external perimeter is 6a and 8a respectively then minimum force to lift up blade from water surface is $x \times 10^{- 2}$ N, then $x$ is (Take a = 10 cm )

The correct option is A 2
Total perimeter $= 14 a$
Force needed to lift blade up
$=$ Surface tension $\times$ Perimeter
$= T \times 14 a$
$= \frac{1}{7} \times 10^{- 1} \times 14 \times 10 \times 10^{- 2} = 2 \times 10^{- 2} N$