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**1. Homework Statement**

Based on your observations of the behavior of your computer model of a planet orbiting a star, and on your reading in the textbook, which of the following statements about an elliptical orbit are true?

At any instant the momentum of the planet is tangent to the planet's trajectory.

The magnitude of the planet's momentum is constant.

The direction of the planet's momentum is changing at every instant.

The gravitational force on the planet due to the star always acts at a right angle to the planet's momentum.

At every instant, d/dt points from the planet to the star.

**2. Homework Equations**

**3. The Attempt at a Solution**

The correct answer is :

-At any instant the momentum of the planet is tangent to the planet's trajectory.

-The direction of the planet's momentum is changing at every instant.

-At every instant, d/dt points from the planet to the star.

Although I do not understand why at every instant, d/dt from the planet to the star.

Can someone please explain this to me?