A Rock Is Whirled on the End of a String

Multiple Choice

A rock is whirled on the end of a string in a horizontal circle of radius R with a constant period T. If the radius of the circle is reduced to R/3, while the period remains T, what happens to the centripetal acceleration of the rock?

A) The centripetal acceleration remains the same.
B) The centripetal acceleration increases by a factor of 3.
C) The centripetal acceleration increases by a factor of 9.
D) The centripetal acceleration decreases by a factor of 3.
E) The centripetal acceleration decreases by a factor of 9.