College Physics (4th Edition)

We can find an expression for the speed when the catapult is stretched a distance $d$: $\frac{1}{2}mv^2 = \frac{1}{2}kd^2$ $v = d~\sqrt{\frac{k}{m}}$ We can find an expression for the speed when the catapult is stretched a distance $3d$: $\frac{1}{2}mv_2^2 = \frac{1}{2}k(3d)^2$ $v_2 = 3\times d~\sqrt{\frac{k}{m}}$ $v_2 = 3v$ The correct answer is: (c) 3v