Please help me with my physics subject please! please! thankszz....?

Question

a planet is moving at constant speed in a circular orbit around a star. In one complete orbit, what is the net amount of work done on the planet by the stars gravitational force; positive, negative, or zero? What if the planet's orbit is an ellipse, so that the speed is not constant?

Answer 1

In a circular orbit the work done is zero because the direction of force is at right angles to the direction of movement.