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Wave Speed

  • Thread starter tdk
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  • #1
tdk
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Homework Statement


A group of swimmers is resting in the sun on an off shore raft. They estimate that 2.2 m seperates 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?
 
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Answers and Replies

  • #2
Dick
Science Advisor
Homework Helper
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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?
 
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  • #3
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You need to calculate how many crests pass per second, then multiply by wavelength. This gives distance/time which is a velocity.
 
  • #4
Astronuc
Staff Emeritus
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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.
 
  • #5
tdk
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Ok so would I do 4.4 x 31? Or do I have to incorporate the 18 in there somewhere?
 
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  • #6
tdk
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Sorry guys I know Im like kinda slow at this, I just suck really bad at physics and math in general really
 
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  • #7
Moonbear
Staff Emeritus
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tdk, I've been trying to get your attention privately, but am going to have to interrupt here publicly. I can't keep deleting that link for you. Your computer must be infected with a virus and I really don't want someone else inadvertently being infected with it through our site. Please run a virus/adware/spyware scan ASAP and clean up your computer.

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

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