A small sphere of mass m is dropped from a great height. After it has fallen 100m, it attains the terminal velocity and continues to all at that speed. The work done by the air friction against the sphere during first 100m is

Options

A. equal to 100 mg
B. greater than 100 mg
C. less than work done by air friction in the section 100 m fall
D. more than the work done by air friction in the second 100 m fall

Answer

C

Explanation

As the sphere falls through air, its velocity goes on increasing till it attains its maximum value v (i.e.,termnal velocity) . Air friction (i.e., viscous force) which is proportional to velocity also increases, as `F=6 pi eta r v :. F prop v` , and ac cordingly more work is done as the sphere falls with a constant velocity v. Thus, less work is done by air friction in first 100 m than in the second 100 m.