Question

A ball on the end of a string is being swung in a horizontal circle or radius, $R$ with a constant speed, $S$.
Which of the following statements best describes the relationship between the velocity of the ball and the net force acting on the ball?

• A. The net force acting on the ball is in the same direction as the velocity of the ball
• B. The net force acting on the ball is opposite in direction as the velocity of the ball
• C. The net force is equal to zero because the object is travelling at a constant speed
• D. The net force is always perpendicular to the velocity vector at all points and always points outward
• E. The net force is always perpendicular to the velocity vector and always points inward

Answer 1

Answer: (E)

The net force is always perpendicular to the velocity vector and always points inward

Since the ball is moving with a constant speed $S$ therefore its tangential acceleration is zero hence no force in tangential direction . Now as the ball is in a circular path so it has centripetal force which is always toward the center of circular path of the ball and perpendicular to the velocity which is along the tangent on the circle at any point .Therefore net force is always perpendicular to the velocity vector and at all points and always pointed inward .