It takes a force of 15 N to stretch an ideal spring of negligible mass 3.0 cm. The spring is placed on a
frictionless horizontal tabletop with one end fixed. A small 50-g metal ball is placed at the free end.
By how much should the spring be compressed to set the ball
in motion horizontally at a speed of
4.5 m/s?
A) 21 cm
B) 4.5 cm
C) 2.1 cm
D) 9.0 cm
E) 4.2 cm