A communication satellite of mass m moves in a stable circular orbit of radius R…
PHYSICS · Multi-part · A Level · Physics · Mechanics and materials · Mechanics and materials
Problem
A communication satellite of mass m moves in a stable circular orbit of radius R around Earth. At every instant the satellite’s speed is v, and the only significant force acting on it is Earth’s gravitational attraction, which is directed toward Earth’s center.
(a) Is the instantaneous mechanical power associated with the gravitational force on the satellite zero, positive, or negative? Explain your reasoning.
(b) Over one complete orbit, what is the average mechanical power associated with the gravitational force? Justify your answer in terms of the satellite’s mechanical energy.
(c) A thruster on the satellite fires briefly in a direction perpendicular to the satellite’s instantaneous velocity, changing only the orbit’s radius but not its speed at that instant. Describe qualitatively whether the thruster delivers non-zero instantaneous mechanical power during the firing, and support your answer with reasoning involving the direction of the force and the velocity.