The equation of a wave is given by `y=10 sin ((2pi)/45 t+alpha)`. If the displacement is 5 cm at `t=0`, then the total phase at `t=7.5` s is

Options

A. `pi/3`
B. `pi/2`
C. `pi/6`
D. `pi`

Answer

B

Explanation

Given `y=10 sin [(2pi)/45 t+alpha]`
`y=5 cm` at `t=0`
`:. 5=10 (sin alpha)`
or `sin alpha =1/2` or `alpha =pi/6`
Again if `t=7.5 s`
Then, total phase `=(2pi)/45xx15/2+pi/6=pi/3+pi/6`
`=(2 pi +pi)/6=(3pi)/6=pi/2`