The amplitude and the time period in a S.H.M. is 0.5 cm and 0.4 sec respectively. If the initial phase is `pi//2` radian, then the equation of S.H.M. will be

Options

A. `y=0.5 "sin" (5 pi t)`
B. `y=0.5 "cos" (5 pi t)`
C. `y=0.5 "sin" (2.5 pi t)`
D. `y=0.5 "cos" (2.5 pi t)`

Answer

B

Explanation

`y=A "sin"g (omega t + alpha)=0.5 "sin" [(2pi t)/(0.4)+(pi)/(2)]`
`= 0.5 "sin" [5 pi +(pi)/(2)]=0.5 "cos" 5 pi t`