Question

Which of the following is true about a planet orbiting a star in uniform circular motion? A. The direction of the velocity vector is always changing. B. The velocity of the planet is constant. C. The speed of the planet is always changing. D. The acceleration vector of the planet points directly away from the star.

Answer 1

Answer;

A.The direction of the velocity vector is always changing.

Explanation;

-A circular orbit of a planet around a star is an example of uniform circular motion (its speed remains constant).

--When a planet has just the right speed (for a given radius of orbit), then it will travel in circular motion with a constant speed. This is called uniform circular motion. Note that the velocity vector changes direction although the speed is constant. This means that there must be a net force on the planet.

Answer 2

As it is uniform circular motion therefore speed is constant. Therefore we can rule out option B. Also in circular motion the direction of velocity vector changes therefore velocity can't be constant. Therefore option B is incorrect as well. Also centripetal acceleration is always towards the center so option D is wrong as well. That implies option A is correct.