question_answer

The displacement of a particle executing S.H.M. is \[y=a\,\sin \,(\omega t-\phi ).\] The velocity of the particle at time \[t=\frac{\phi }{\omega }\] is:

A)  \[\omega \,\cos \,\phi \]                                                            

B)  \[a\omega \]                   

C)         \[\omega \,\cos \,2\phi \]          

D)         \[-a\omega \,\cos \,2\phi \]