Water is following in a river. If the velocity of a layer at a distance 10 cm from the bottom is 20n cm/s. Find the velocity of layer at a height of 40 cm from the bottom.

Options

A. 10cm/s
B. 20cm/s
C. 30cm/s
D. 80 cm/s

Answer

D

Explanation

As `F= - eta A (dv)/(dx)`
`:. F prop (dv)/(dx) or F prop (Delta v)/(Delta x)`
or `F prop (v)/(x)` (since, velocity of the layer at the bottom is zero)
or `x prop (v)/(F)`
But F is constant, so `x prop v`
`:. (v_(2))/(v_(1)) = (x_(2))/(x_(1)) or (v_(2))/(20) = (40)/(10) or v_(2) = 80cm//s`