Step 1: Formula for maximum force in SHM.
\[
F_{max} = m\omega^2 A
\]
Step 2: Given values.
\[
m = 0.7\,kg,\quad A = 7\,cm = 0.07\,m,\quad T = 0.2\,s
\]
Step 3: Find angular frequency.
\[
\omega = \frac{2\pi}{T} = \frac{2\pi}{0.2} = 10\pi
\]
Step 4: Compute \(\omega^2\).
\[
\omega^2 = 100\pi^2 \approx 986.96
\]
Step 5: Substitute values.
\[
F_{max} = 0.7 \times 986.96 \times 0.07
\]
Step 6: Final calculation.
\[
F_{max} \approx 48.3\,N
\]
Final Answer:
\[
\boxed{48.3\,N}
\]