Answer
(a) simple harmonic,
(b) $6\ m$,
(c) $2\ sec$,
(d) $\frac{1}{2}\ Hz$.
Work Step by Step
(a) Given $d=6cos(\pi t)$, we can describe the motion of the object as simple harmonic,
(b) The maximum displacement from its resting position can be found as $6\ m$,
(c) We can find the period as $p=\frac{2\pi}{\pi}=2\ sec$,
(d) The frequency is the reciprocal of the period $f=\frac{1}{p}=\frac{1}{2}\ Hz$.
