which of the following statements about an elliptical orbit are true?

Question

1.At any instant the momentum of the planet is tangent to the planet's trajectory.
2. At every instant, d/dt points from the planet to the star.
3.The gravitational force on the planet due to the star always acts at a right angle to the planet's momentum.
4.The direction of the planet's momentum is changing at every instant.
5. The magnitude of the planet's momentum is constant.

Answer 1

124

Answer 2

(5) is true for two body problems only. None of the other are true in general.

Although you really need to specify you mean angular momentum or linear momentum to make the question clear.

Answer 3

I think 4 and 5 both will combine to give the correct answer. As those two points are self explanatory so there is no explanation required for that.

Answer 4

4 Is true unless the orbit is a degenerate ellipse with no width.

Answer 5

1,2,4, are true for an elipse
3,5 are true only for a circular orbit.