Wave Speed: Calculating with 2.2 m & 31 s

[tdk]

Homework Statement

A group of swimmers is resting in the sun on an off shore raft. They estimate that 2.2 m separates a trough from an adjacent crest of surface waves on a lake. They count 18 crests that pass by the raft in 31s. How fast are the waves moving?

Homework Equations

F= 1/t v=wavelength x frequency

The Attempt at a Solution

2.2(2)=4.4= wavelength

4.4 x 31? or 4.4 x 18? or something else?

 

[Dick]

I think pugfug was being alarmist about the link. Welcome back. Sorry about the panic. Anyway we now want frequency, the number of wavelengths per second. How many wavelengths in 31 secs?

 

[Mentz114]

You need to calculate how many crests pass per second, then multiply by wavelength. This gives distance/time which is a velocity.

 

[Astronuc]

2.2(2)=4.4= wavelength

Correct. The wavelength is twice the peak-to-trough distance.

Now speed is length/time, so find the total length of the waves passing the raft in t=31s.

 

[tdk]

Ok so would I do 4.4 x 31? Or do I have to incorporate the 18 in there somewhere?

 

[tdk]

Sorry guys I know I am like kinda slow at this, I just suck really bad at physics and math in general really

 

[Moonbear]

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Folks, do NOT click on that link no matter how tempted. It apparently contains a virus.