When two sound waves with a phase difference of $\pi / 2$ and each having amplitude $A$ and frequency $\omega$ are superimposed on each other, then the maximum amplitude and frequency of resultant wave is $\quad$ [MP PMT 1989]
(a) $\frac{A}{\sqrt{2}} ; \omega / 2$
(b) $\frac{A}{\sqrt{2}} ; \omega$
(c) $\sqrt{2} A ; \frac{\omega}{2}$
(d) $\sqrt{2} A ; \omega$