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A matchstick 5 cm long floats on water. The water film has a surface tension of 70 dyn/cm. A little comphor put on one side of stick reduces the surface tension there to 50 dyn/cm. The net force on the matchstick is (A) 4 dynes (B) 20 dynes (C) 100 dynes (D) 600 dynes. |
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Answer» Correct Option is (C) 100 dynes l = 5 cm \(T_1 = 70\) dyne / cm \(T = \frac{F}{l}\) \(F_1 = T . l\) \(F_1 = 5 \times 70\) \(F_1 = 350\) dyne ............. \((F_1)\) \(F_2 = T_2 .l\) \(F_2 = 50 \times 5\) \(F_2 = 250\) dyne .............. \((F_2)\) Net. force = \(F_1 -F_2\) = 350 - 250 = 100 dynes (C) 100 dynes |
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