How do I set up this problem (finding wave frequency)

"A cork floating on water moves up and down 10 times in 30 seconds. What is the frequency of the water wave?"

I know the formula for frequency but I'm not sure what to do with those two values.

Thanks.

See, that's the problem with memorizing equations, but having no clue about the physics. Let's have a bit of a physics lesson shall we?

We start with the basic distance = average speed X time traveled. When that distance is the length of one wave, L, we can write L = Vavg T. And when L is the wavelength, T is the period by definition because that's the time it takes the wave to travel one wavelength.

Now we can change the name of one wavelength into one cycle. Cycle and wavelength are just two different measures for the same thing, the distance between two ups or between two downs in your case. That distance is one cycle. Now you know the physics, here's your problem.

You have 10 ups or 10 downs. So you have nine cycles. Do you see that? Here: u u u u u u u u u u; 10 ups. But there are only nine wavelengths, one wavelength from the first u to the second, from the second to the third, etc. Nine intervals, nine cycles.

So we have L = 9 = Vavg T = Vavg 30; where T = 30 seconds for those nine cycles to pass. And so you have Vavg = L/T = 9 cycles/30 seconds = .3 cycles/second which is the frequency. ANS. And as you can plainly see, frequency is just the average speed of a wave in cycles per second.

I strongly recommend you study physics by learning the physics, not by memorizing the equations. And the first step in learning the physics is in learning the definitions; in this case, Vavg = L/T = F the frequency when L is length in cycles and T is the total time for L cycles to pass.

Also note that L <> 10 ups as this is the number of crests, not the number of wave lengths or cycles. So 10/30 = .33 <> F as it overstates the frequency.

<> means, does not equal. This is a standard symbol used in computer language and spreadsheets like Excel. Related are >= greater than or equal; <= less than or equal. And < x for less than x, > x for greater than x.

Report Abuse

I forgot to add. ~ the tilda is often used as "approximately." So 3 ~ 3.14159, three is approximately 3.14159. But watch this one as it's also often used for proportional. So g ~ M/r^2, g is proportional to M over r^2.

Report Abuse

Frequency is the number of vibrations(or cycles) per unit of time, therefore f = 10 times / 30 secs
f = 10/30 = 0.3 cycles per sec or 0.3 cps