Question

A plate of area 10 cm² is placed over a plane. A layer of glycerine of mm thickness is lying between two plates. To move the upper plate with velocity 10 m/s, the required external force is ................ (η for glycerine = 20 poise)
(A) 80 dyne
(B) 800 dyne
(C) 200 × 10³ dyne
(D) 2000 × 10³ dyne

Answer 1

Answer:

200 × 10³ dyne...........

Answer 2

Answer:

(C) 200 × 10³ dyne

Explanation:

In the question, the given values are

Area of plate= 10 $cm^{2}$

or, =0.001  $m^{2}$

thickness pf layer= 1 mm = 0.001 m

velocity = 10 m/s

and viscosity = 20 poise

we know that,

1 poise= 0.01 Pa.s

1 Dyne =0 .00001 Newton

Formula for the required external force is

$F=η A\frac{dv}{dx}$

Putting the values of all the given data in the above formula,we get

$F= 20*(0.01 Pa.s)*0.001 m*\frac{10m/s}{0.001}$

Now, solving the equation, we get

F=2 Newton

we know that

1 Dyne =0 .00001 Newton

so,

F= $\frac{2}{0.00001} Dyne$

F= $200*10^{3} dyne$