# Waves and Energy transfer problem ( am desperate)

1. Apr 11, 2005

### Alexielle

Waves and Energy transfer problem (plz am desperate)

Well, this is the problem that is breaking my head

the time needed for a water wave to change from the equilibrium level to the crest is 0.18s
a) what fraction of a wavelength is this?
b)what is the period of the wave?
c)What is the frequency of the wave?

I dont really understand this problem because of the little information they give me, and the fact that when i tried to check it with my brother's answer book, the wavelength gave 1/4, but they do not give a formula or say why the WL is 1/4..

2. Apr 11, 2005

### theCandyman

A) Think a little, the whole wavelength would be measured from crest to crest. Let us use the sine wave as an example going from 0 to $$2\pi$$. Compare the distance from where the function equals zero (in your wave example, this is the equlibrium point) to where it equals 1 (again, in your example the crest) and then campare it to the entire wavelength of the function.

B) If it takes 0.18 seconds for one fourth of a wavelength to travel, how long does it take the whole wavelength?

C) Frequency is the inverse of the time, $$f=1/T$$.

3. Apr 12, 2005

### HallsofIvy

Staff Emeritus
Draw a picture! A wave starts from 0, goes up to its highest point, back down to 0, then down to its lowest point, then back up to 0: four sections, each of the same length- the whole thing is one wave length. Since you given ONE of the 4 sections (from 0 up to its highest point) you are given 1/4 of the entire wavelength.

Since 1/4 of the entire wavelength takes 0.18s, the entire wavelength will take
4(0.18)= 0.72 s, the period of the wave.

As theCandyman said, the frequency is 1 over the period: 1/0.72 "cycles per second"