Simple Harmonic Motion - Conflicting equations!

  • Thread starter jumbogala
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  • #1
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Homework Statement


What is the equation for the displacement of a sin wave (eg something in SHM)?

My book says x(t) = Acos(ωt + ɸ0)

My prof's notes say y(x,t) = Asin(ωt - kx + ɸ0)


Homework Equations





The Attempt at a Solution


I'm not confused about why one is sin and the other is cos. I'm confused why one has the extra term -kx. When do you use which?

I have a question that asks me to write the displacement for a sine wave travelling to the left with frequency 200 Hz, speed 400 m/s, amplitude 0.010 m, and initial phase 90 degrees. So I'm not sure which of the above to use.
 

Answers and Replies

  • #2
rl.bhat
Homework Helper
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First one is the general equation of SHM.
The second one the equation of the sine wave propagating in a medium towards the positive x direction.
You have to use the second equation to find the displacement with a small modification.
 

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