State the condition in which gravitational potential energy is said to be (i) Negative, (ii) Positive.

Explanation

`W=U(r)-U(r')`
(i) If `rltr'`
Since gravitational force is attractive, since a body of mass `m_(2)` is attracted by another body is mass `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) If `rgtr'`
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.