The velocity of water in a river is 18kmph near the surface. If the river is 4m deep, the shearing stress between horizontal layers of water in Nm−2 is (ηwater=1×10−3pa.s):
A
2.5×10−3
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B
12.5×10−3
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C
0.75×10−3
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D
zero
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Solution
The correct option is B12.5×10−3 Force = ηAdvdy Shearing stress =ηdvdy Now, dvdy=18×1000×10004m×3600S−1=1.25S−1