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When does the work done to be negative a...

When does the work done to be negative and positive?

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(i) Case 1: If `r < r' Since gravitational force is attractive, `m_(2)` is attracted by `m_(1)`. Then `m_(2)` can move from `r' ` to r without any external work. Here work is done by the system spending its internal energy and hence the work done is said to be negative.
(ii) Case 2 : If r > r' Work has to be done against gravity to move the object from r' to r. Therefore work is done on the body by external force and hence work done is positive.
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