SAT Subject Physics Practice Question 556: Answer and Explanation
12. An object is moving in a circular path with a constant velocity (v). If the radius of the circle in which the object is moving is decreased by one half and the velocity remains the same, what will happen to the centripetal force?
A. It will be 4F.
B. It will be 2F.
C. It will be F.
D. It will be F/2.
E. It will be F/4.
Correct Answer: B
The correct answer is (B). Since the centripetal force is found with the equation Fc = (m)(v2)/r we can change the r value to .5r and substitute it into the equation and solve to find the relative force. Fc = (m)(v2)/.5r. Clearly the force will be double when the radius is halved and the velocity remains the same.