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If $y_1=A\sin(\omega t-kx)$ and $y_2=A\sin(\omega t+kx)$ are superposed, the resultant displacement is

A$y=2A\sin\omega t\sin kx$
B$y=2A\cos\omega t\cos kx$
C$y=2A\sin\omega t\cos kx$
D$y=A\sin\omega t$
Answer & Solution
Correct answer: C. $y=2A\sin\omega t\cos kx$
Using $\sin C+\sin D=2\sin\frac{C+D}{2}\cos\frac{C-D}{2}$, with $C=\omega t-kx$ and $D=\omega t+kx$, we get $$y=2A\sin\omega t\cos kx.$$ This is the standard equation of a standing wave.
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