A slingshot consists of a light leather cup containing a stone. The cup is pulled back against two parallel rubber bands. It takes a force of 15 N to stretch either one of these bands 1.0 cm.
(a) What is the potential energy stored in the two bands together when a 40-g stone is placed in the cup and pulled back 0.15 m from the equilibrium position?
(b) With what speed does the stone leave the slingshot?