Explanation:
Given, \(A = 10\;cm = 0.1\;m,\,\,T = 4\;s,\,\,t = 1\,\;s.\)
Speed of oscillating simple pendulum is given by
\(v = \frac{{dy}}{{dt}} = v = A\omega \,\,\cos \,\,\omega t\)
\(({\text{as}}\,\,y = A\,\,\sin \,\,\omega t)\)
\( = A \times \frac{{2\pi }}{T}\cos \left( {\frac{{2\pi }}{T}t} \right)\)
\( = \frac{{2\pi \times 0.1}}{4}\,\,\cos \,\,\left( {\frac{{2\pi \times 1}}{4}} \right)\)
\( = \frac{{2\pi \times 0.1}}{4}\,\,\cos \frac{\pi }{2} = 0\)