- #1

- 276

- 4

## Homework Statement

I seem to have problems finding time in SHM.

To find the time after projection, I know that either x=asinωt or x=acosωt needs to be used, so since R is projected away from O, it means that it is moving towards the equilibrium position, therefore I used x=acosωt to find the time.

## Homework Equations

x=asinωt x=acosωt

## The Attempt at a Solution

x=acosωt

-L/4 = 3L/4 cos (√2g/L)t

t= (√L/2g) cos

^{-1}(-1/3)

But, the correct answer should be

t=(√L/2g) sin

^{-1}(1/3)

Why can't cosine be used? Since it is moving

**towards**the equilibrium position?

Also, for the equations x=asin(ωt+α) or x=acos(ωt+α)

I am not sure when is α needed to take into consideration.

So far, I never encountered any questions needing to find α, but I would like to know when is α needed.

Thanks very much in advance!