\(T=0.1\)
\(\omega=20 \pi \,rad / s\)
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