SSC JE Mechanical Engineering 2014 Set 1 Paper

Question : 169 of 200

Marks: +1, -0

The velocity distribution for flow over a flat plate is given by

u = (y – y ^2 )

in which u is velocity in metres per second at a distance y metres above the plate. What is the shear stress value at y = 0.15 m ? The dynamic viscosity of fluid is 8.0 poise.

12.4 N/m $^{2}$
1.24 N/m $^{2}$
0.56 N/m $^{2}$
5.6 N/m $^{2}$

Validate

Solution:

Given:

u = y -y^2

∵ {du}/{dy}=1-2y

=({du}/{dy})_{\at y= .15}=1-2×.15=0.70

at y = 0.15, µ= 8 paise = 0.8 N-S/m

^2

shear stress,

τ={dµ}/{dy}=0.8×0.7=0.56\N.\m^2

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