d
(d)
$T=0.1$
$\omega=20 \pi \,rad / s$
Amplitude $A=0.1 \,m$
$a=-\omega^2 x$
Maximum acceleration $=-\omega^2 A$
Maximum force $=-m \omega^2 A$
$F_{\text {max }}=-0.01 \times(20 \pi)^2 \times 0.1$
$F_{\max }=-0.001 \times 400 \pi^2$
$=-3.95 \,N$
or $-4 \,N$ approximately