# Homework Help: Harmonic Waves help

1. Dec 5, 2004

### bwjohnson9

Hello, I am having a problem solving part B of the following problem

A harmonic wave moving in the positive x direction has an amplitude of 3.8 cm, a speed of 36.0 cm/s, and a wavelength of 38.0 cm.

A) Calculate the displacement (in cm) due to the wave at x = 0.0 cm, t = 2.0 s. Assume that the displacement is zero at x = 0 and t = 0.

B) Calculate the displacement due to the wave at x = 10.0 cm, t = 20.0 s.

I got the answer to the first problem by using the equation
y=A x Sin (w x t)

f=velocity / wavelength = (.36m)/(.38m)= 0.94736

Period (T)= 1 / F = 1/0.94736 = 1.055

w= 2 x Pi/T = 2*pi / (1.055) = 5.9556

x= 2.3cm

This was fairly easy because x=0 and t=2 sec.

But I am not sure what to do when x= 10.cm and t= 20sec

Anybody got any tips?

2. Dec 5, 2004

### saltrock

Just use the formula y=asinwt where a=38 cm

3. Dec 5, 2004

### Pyrrhus

the formula for an harmonic wave

$$y = A \sin (kx - \omega t)$$

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