Pi/2 Translational Difference in y(x,t) Equations

[Helicobacter]

In my text
y(x,t)=Acos(kx-ω t)
In the teacher's handout:
y(x,t)=Asin(kx-ω t)
There's a translational difference of pi/2 between them! I don't know which one to use for the test :S

 

[zergju]

hehe, its just a matter of initial condition (with difference of pi)
and thereotically an ideal sound wave is usually calculated for a stablized value which means the initial condition doesn't matter much.. very seldom do we need to know its initial condition..
so no matter sin or cos will end up with e same results.
and u can use either one u want due to different kinds of calculations

 

[AlephZero]

To be accurate, there's a translational difference of pi/2k between them.

Or looking at it a different way, there is a time difference ot pi/2ω

As zergju says, they both represent "the same wave motion", but measured relative to differet points in space and/or time.

 

[Helicobacter]

That was helpful, thanks