Homework Help: Transverse Waves speed

1. Apr 18, 2007

croyboy

Having a little difficulty with a homework question and concept

1. The problem statement, all variables and given/known data
y = 2.28sin(0.0276pi x + 2.42pi t)

Find the amplitude, wavelength, frequency, speed and maximum transverse speed.

3. The attempt at a solution

A = 2.28cm
Wavelength = 72.46 cm
Frequency = 1.21 Hz

Speed = 87.68 cm/s
Max transverse speed = ??????

Reasoning

The speed should be w/k which would give 2.42pi/0.0276pi = 87.68 cm/s

The max transverse velocity though....would that be when the trig function of cos is equal to 1 in this equation u = -wAcos(kx-wt) ????

Last edited: Apr 18, 2007
2. Apr 18, 2007

Dick

The speed is correct. Transverse speed is when dy/dt is a max. I think you are pretty much nailing that as well.

3. Apr 19, 2007

croyboy

Apologies...still not quite sure.....would I use the w and A i know multiplied with cos(kx-wt) to get my answer.....so if cos(kx-wt)=1, then max transverse speed would be -wA???

4. Apr 19, 2007

mezarashi

If your displacement function is a sin wave, it's not possible that your velocity "function" be a constant of 87.68cm/s as you calculated. Your speed would be a function as well.

As you know, velocity is the change of displacement over time (i.e. dy/dt), so by differentiating the function for y, you will get a the velocity function (which in this case is a cosine function). That cosine function will allow you to calculate the speed at any location x and time t.

To calculate the maximum speed, we take a look at the velocity function. If you do your calculus right, the equation should look something like:

v = B cos (Cx + Dt)

There is an infinite possibility for the values of x and t, so we can assume that hthe cosine can return any value. The maximum value however of a cosine function is 1. So what does that tell you about your maximum velocity?

5. Apr 19, 2007

Dick

Yes. Except I'd call the maximum speed +wA. Why would you say minus?

6. Apr 19, 2007

croyboy

Thanks much....makes a lot more sense.....appreciate the help