#### A small sphere of mass m is dropped from a great height. After it has fallen 100 m, it has attained its terminal velocity and continues to fall at that speed. The work done by air friction against the sphere during the first 100 m of fall is Option 1) Greater than the work done by air friction in the second 100 m Option 2) Less than the work done by air friction in the second 100 m Option 3) Equal to 100 mg Option 4) Greater than 100 mg

As discussed in

Terminal Velocity -

When spherical body attains constant velocity in viscous fluid.

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In the first 100 mts body starts from rest and its velocity goes on increasing and after 100 mts it acquires maximum velocity (terminal velocity) i.e. viscous force which is proportional to velocity.

Hence work done against air friction in first 100 m is less than the work done in next 100 m.

Option 1)

Greater than the work done by air friction in the second 100 m

This solution is incorrect.

Option 2)

Less than the work done by air friction in the second 100 m

This solution is correct.

Option 3)

Equal to 100 mg

This solution is incorrect.

Option 4)

Greater than 100 mg

This solution is incorrect.