Initially,a Small 2

Multiple Choice

Initially,a small 2.0-kg rock is whirling at the end of a very thin string in a circular path of radius 0.75 m on a horizontal frictionless surface,as shown in the figure.The initial tangential speed of the rock was 5.0 m/s.The string has been slowly winding around a vertical rod,and a few seconds later the length of the string has shortened to 0.25 m.What is the instantaneous speed of the mass at the moment the string reaches a length of 0.25 m?

A) 3.9 m/s
B) 9.3 m/s
C) 15 m/s
D) 225 m/s
E) 75 m/s