You are swinging a ball on a string around in a horizontal circle above your head and it moves in that circle at a constant speed. We are neglecting air resistance and gravity. Even though the string is exerting a force on the ball, the ball's energy isn't changing because
A. the negative amount of work that the centripetal force does on the ball is exact cancelled by the positive amount of work that the centrifugal force does on it.
B. the positive amount of work that the centripetal force does on the ball is exact cancelled by the negative amount of work that the centrifugal force does on it.
C. the ball's inertia is conserved.
D. the centripetal force the string exerts on the ball is exactly at right angles to the ball's motion.
Answer:D
You are swinging a ball on a string around in a horizontal circle above your head and it moves in that circle at a constant speed. We are neglecting air resistance and gravity. Even though the string is exerting a force on the ball, the ball's energy isn't changing because
A. the negative amount of work that the centripetal force does on the ball is exact cancelled by the positive amount of work that the centrifugal force does on it. B. the positive amount of work that the centripetal force does on the ball is exact cancelled by the negative amount of work that the centrifugal force does on it. C. the ball's inertia is conserved. D. the centripetal force the string exerts on the ball is exactly at right angles to the ball's motion.