Question

A circular metal plate of radius 5 cm rests on a layer of centre oil 2mm thick whose coefficient of viscosity is 15.5 dyne $ c{{m}^{-2}}s $ . The value of shearing stress when a horizontal force move the plate with a speed of 5 cm/s will be

• A. 387.5 dyne $ c{{m}^{-2}} $
• B. 328 dyne $ c{{m}^{-2}} $
• C. 250 dyne $ c{{m}^{-2}} $
• D. 428 dyne $ c{{m}^{-2}} $

Answer 1

Answer: (A)

Shearing stress $ =\eta \times $ strain rate $ =\eta .\frac{dv}{dx}=15.5\times \frac{5}{0.2}=387.5dyne\text{ }c{{m}^{-2}} $