Question

There is a 1 mm thick layer of glycerine between a flat plate of area 100 cm² and a big plate. If the coefficient of viscosity of glycerine is 1.0 kg(m-s), then how much force is required to move the plate with a velocity of 7 cm/s ?

(1) 0.7 N 

(2) 7 N

(3) 35 N 

(4) 3.5 N

Answer 1

Correct Answer is: (1) 0.7 N 

To move the plate with a constant velocity, the necessary force will be equal to the viscosity force F(say). Now