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