ICSE Class 10 Answered

Answer

(A) is true but (R) is false

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when the mass tied at end of string is rotated, initially it moves from lower position to top position.

In this upward motion work is done externally on mass . Hence work done on mass is positive and magnitude of work equals change in potential energy

When the mass moves downward from top position to lower position work is done by gravitational field .

Hence work done on mass is negative and magnitude of work done equals change in potential energy.

Hence net work done in a circular motion is zero.

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There is no drag force and air resistance is negligible in vacuum .

Hence workdone due to drag force is zero in vacuum.