**Answer to question:**

Work done by external forces (excluding gravitational force) is negative.

Since for satellites in orbit (where *G *is the gravitational constant, *r* is the radius of the orbit, *M* is the mass of the planet and *m* is the mass of the satellite), kinetic energy increases. Hence is positive.

**Work done by gravity is positive** as the radial displacement is in the same direction as that of the force. Work done by gravity =

According to the Work-Energy Theorem, net work = work done by gravity + work done by external force = . Hence, work done by external force = .