b
(b)
$x=5 \cos (2 \pi t+\pi / 4)$
$t=\frac{3}{2} s$
$x=5 \cos (3 \pi+\pi / 4)$
$x=5 \cos \left(\frac{13 \pi}{4}\right)$
$x=-5 \cos \frac{\pi}{4}$
$x=-\frac{5}{\sqrt{2}}$
Acceleration
$a=-\omega^2 x$
$a=-4 \pi^2 x-\frac{5}{\sqrt{2}}$
$a=139.56 \,m / s ^2$