$\bullet\bullet$ A mass-spring system is in SHM in the horizontal direction. If the mass is $0.25 \mathrm{~kg}$, the spring constant is $12 \mathrm{~N} / \mathrm{m},$ and the amplitude is $15 \mathrm{~cm}$
(a) what is the maximum speed of the mass, and
(b) where does this occur?
(c) What is the speed at a half-amplitude position?