MCQ
The resultant of two rectangular simple harmonic motions of the same frequency and unequal amplitudes but differing in phase by $\frac{\pi }{2}$ is
  • A
    Simple harmonic
  • B
    Circular
  • Elliptical
  • D
    Parabolic

Answer

Correct option: C.
Elliptical
c
(c)If first equation is ${y_1} = {a_1}\sin \omega \,t$

==> $\sin \omega \,t = \frac{{{y_1}}}{{{a_1}}}$ ... (i)
then second equation will be ${y_2} = {a_2}\sin \left( {\omega \,t + \frac{\pi }{2}} \right)$
$ = {a_2}\,\left[ {\sin \omega \,t\cos \frac{\pi }{2} + \cos \omega \,t\sin \frac{\pi }{2}} \right] = {a_2}\cos \omega \,t$
==> $\cos \omega \,t = \frac{{{y_2}}}{{{a_2}}}$ ... (ii)
By squaring and adding equation (i) and (ii)
${\sin ^2}\omega \,t + {\cos ^2}\omega \,t = \frac{{y_1^2}}{{a_1^2}} + \frac{{y_2^2}}{{a_2^2}}$
==> $\frac{{y_1^2}}{{a_1^2}} + \frac{{y_2^2}}{{a_2^2}} = 1$; This is the equation of ellipse.

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