Which of the following correctly explains why the gravitational potential energy of a satellite in orbit around Earth is negative?
(a) Because the gravitational force is attractive and therefore assigned a negative sign; this negative sign directly carries over to the potential energy value.
(b) Since zero potential energy is chosen at Earth’s surface, any point above the surface, including the satellite’s orbit, must have a negative potential energy.
(c) Work must be done against Earth’s attraction to bring the satellite from infinity (taken as the zero level) to the orbit; therefore the potential energy at the orbit becomes negative.
(d) In order for the total mechanical energy of an orbiting satellite to be zero, the kinetic energy (positive) must be balanced by a negative potential energy value.