Two students watch the waves produced by a wave machine at a swimming pool. One student walks beside a wave as it travels along the pool. The wave goes from one end of the pool to the other in 20s. The length of the pool is 24m
A) Calculate the speed of the waves.
I already have the answer for that part - 1.2 ms
B) in the same time interval, the other student counts 5 waves going past the point where he is standing. Calculate the frequency of the waves.
I know to find the frequency you divide speed by wavelength. However, the solution is written in the book I've got the question from and it says, f=5/20, which gives 0.25Hz. This answer Is confirmed at the back of the book. I don't understand how this is correct.
Can somebody please explain it to me?
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For starters, your wave speed is 1.2 m/s, not 1.2 ms. (Meters per second, not Meter-seconds.)
> I know to find the frequency you divide speed by wavelength.
That's correct, but you don't have the wavelength. You don't need that formula. But you know that the second student counted 5 waves (cycles), in 20 seconds. So, to calculate the frequecy (in cycles per second), you divide the number of waves counted by the time interval. That's the 5/20 = 0.25 cycles /second.
You can now calculate the wavelength, if you want to.
frequency is the reciprocal of the time period, you just use the 1/x key on your calculator, i:e 0.2sec = 5hz, 0.02sec = 50hz.
if you divide 20/5 you get 4 and the reciprocal is 0.25.
20s/24m = 0.8333333333 1/x = 1.2
as there are 5 waves the waves occur one every 4 seconds (20/5)and 4 1/x = 0.25