Mathematics I / Energy and Conservation Laws
Practice question · True or false

Gravity does no work on a satellite in a circular orbit.

Hints
  1. What angle does the force make with the motion?
  2. Work needs a component along the displacement.
Show the answer

True

Why

True. The gravitational force points to the centre while the velocity is tangential, perpendicular at every instant, so W=Fdcos90°=0W = Fd\cos 90° = 0 and the speed never changes. In an elliptical orbit they are not perpendicular, which is exactly why such a satellite speeds up near perigee.

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