Question

We have three beakers A, B and C containing glycerine, water and kerosene respectively. They are stirred vigorously and placed on the table. The liquid which comes to rest at the earliest is
A. Glycerine
B. Water
C. Kerosene
D. All of them at the same time.

Answer 1

Hint: When adjacent layers of the fluid are in relative motion with respect to each other or tend to have relative motion, then the viscous force acts between the layers which oppose the relative motion.

Complete step by step solution:
We have given three beakers A, B and C.
Beaker A has glycerine.
Beaker B has water.
Beaker C has kerosene.
They are stirred vigorously then we need to compare the time taken by all the fluids to come to rest in order to determine the liquid which comes to rest at the earliest.

The force which opposes the relative motion between the layers of the fluid is called viscous force. The coefficient of viscosity is the molecular property of the fluid. Greater will be the coefficient of viscosity, greater will be the viscous force opposing the relative motion between fluid layers.

As the coefficient of viscosity for the glycerine is greater than that of water and kerosene. So, the viscous force in the glycerine is the largest of all the other fluids given. The viscous force is a resistive force which opposes the relative motion between the layers of the fluid.

As we know that the rate of change of velocity is directly proportional to the magnitude of the force acting on it. The magnitude of deceleration is largest in glycerine out of water and kerosene. So, the relative motion between the layers of Glycerine is greatly opposed by the viscous force, so it will come to rest earlier than the water and the kerosene.

Therefore, the correct option is A.

Note: With the change in temperature the coefficient of viscosity changes. So, all the beakers should be at the same temperature to determine which fluid will come to rest earliest.