Identify the nature (sign) of work that must be done by an external agent to slowly lower a satellite from a higher circular orbit of radius 5R to a lower orbit of radius 3R around Earth (take R as Earth’s radius, neglect atmospheric drag).
(a) Negative, because energy is released as the satellite moves to a lower orbit
(b) Positive, because the satellite’s speed increases and this extra kinetic energy must be supplied
(c) Zero, because the decrease in gravitational potential energy exactly equals the increase in kinetic energy
(d) Cannot be predicted without knowing the satellite’s mass and actual energies