Fluid Mechanics Viscosity Question 121
Question: Velocity of water in a river is[CBSE PMT 1988]
Options:
A) 2
B) 3
C) 4
D) $ 2\sqrt{2} $
Show Answer
Answer:
Correct Answer: C
Solution:
$ t=\frac{A}{a}\sqrt{\frac{2}{g}}\left[ \sqrt{H_{1}}-\sqrt{H_{2}} \right] $ Now, $ T_{1}=\frac{A}{a}\sqrt{\frac{2}{g}}\left[ \sqrt{H}-\sqrt{\frac{H}{\eta }} \right] $ and $ T_{2}=\frac{A}{a}\sqrt{\frac{2}{g}}\left[ \sqrt{\frac{H}{\eta }}-\sqrt{0} \right] $ According to problem $ T_{1}=T_{2} $ $ \sqrt{H}-\sqrt{\frac{H}{\eta }}=\sqrt{\frac{H}{\eta }}-0 $ Þ $ \sqrt{H}=2\sqrt{\frac{H}{\eta }}\Rightarrow \eta =4 $
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