State, whether the work done in the following cases, is positive or negative.
Work done by resistive force of air on a pendulum bob to bring it to rest.

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Solution

The pendulum is already in motion, and a force is applied to bring it to rest.
The force is resistive and acts in the opposite direction of the motion of the body. The angle in between them is 180 degrees.
$W o r k d o n e = F o r c e \times D i s p l a c e m e n t \times A n g l e b e t w e e n t h e m W = F S \cos θ f o r W = - v e = \cos θ = - v e$
Hence, the work done by the resistive force of air on a pendulum bob to bring it to rest is negative.

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State, whether the work done in the following cases, is positive or negative.Work done by resistive force of air on a pendulum bob to bring it to rest.

State, whether the work done in the following cases, is positive or negative.
Work done by resistive force of air on a pendulum bob to bring it to rest.