# Speed of progressive waves numerical

1. Jun 29, 2012

### lionel messi.

1. The problem statement, all variables and given/known data:
progressive waves of frequency 300 hz are superimposed to produce a system of stationary waves in which adjacent nodes are 1.5m apart.calculate speed of progressive waves?

2. The attempt at a solution:
should i use
1)v=f*λ=300m/s
or
2)v=f*(2λ)=900m/s

2. Jun 29, 2012

### collinsmark

Be careful here.

The symbol for wavelength is pretty much always denoted as λ. And the velocity of a wave is always v = λf (where f is the frequency). This relationship wasn't used correctly in 2), given your choice of variable names.

(Not to mention that the math in 1 isn't right either; 300 x 1.5 ≠ 300)

What you should be asking yourself is "how many nodes occur in one wavelength?"

Try plotting cos x on a piece of paper. Don't forget to put the x-axis and y-axis on the plot. From one peak to the next peak of the function (one wavelength), how many times does the function cross the x-axis?

3. Jun 30, 2012