(a) The given equation is
$y = 5\sin{\frac{\pi}{2}(100t - x)}\ \ \ldots(i)$
Comparing Eq. (i) with standard wave equation, given by
Y=a sin (ωt-kx) …(ii)
We have
$\omega = \frac{100\pi}{2} = 50\pi$
$\Longrightarrow \ \frac{2\pi}{T} = 50\pi$
$\Longrightarrow T = \frac{2\pi}{50\pi} = 0.04\ s$