aamc #5: PS-Question 9

[loreben]

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Hi SDNers,
I hope you are all having a great weekend. I have a question that i need some help with. Please see the question below:

If ocean waves strike the shore every 3seconds and the horizontal distance between adjacent crests and troughs is 1m, What is the average speed of the waves?

Thanks 🙂

N:B- I want mainly some clarification on what value you decided the wavelength to be and the reason for choosing that value. My mind is stuck on it being a different value which is not the right value to use.

 

[cartman1980]

If ocean waves strike the shore every 3seconds and the horizontal distance between adjacent crests and troughs is 1m, What is the average speed of the waves?

I'll give it a first shot (Since over 5 mins were spent to understand the question, answer may be incorrect) 🙂

I interpreted this question to mean
- distance between two successive crests is 1m AND
- distance between two successive troughs is 1m

(Start of #1)<-- 0.5 --> (Crest#1)<-- 0.5 --> (trough#1:END)<-- 0 -->(Start of #2) <-- 0.5 --> (Crest#2)<-- 0.5 --> (trough#2:END)

end of trough of #1 is beginning of #2 since distances for both crests and troughs are given to 1m.

Assuming
- When ocean wave strikes the short, the trough makes contact w/ shore
AND
- time between strikes is 3 seconds
AND
- no distance between two successive waves

v = d/t
v = (distance from START:trough#1 to END:trough#1) / 3
v = 1 /3 m/s

 

[loreben]

🙂, That was the same approach i applied but the answer is incorrect. The wavelength is a different value.

Thanks though for your response

 

[rrmix]

wavelength should be 2m, because wavelength is from crest to crest or trough to trough. So the answer should be 2/3 ?

 

[cartman1980]

That was the same approach i applied but the answer is incorrect. The wavelength is a different value.

Atleast, now i know my conceptual understanding of wavelength is incorrect. Back to the drawing board (and there goes another hour or my life) 🙂

wavelength should be 2m, because wavelength is from crest to crest or trough to trough.

If wavelength is crest-crest OR trough-trough, then why 2? Since it is given that distance between adjacent crests and troughs is 1m, shouldn't wavelength be 1?

 

[rrmix]

Creast to Trough is 1 M, then you have to go from the trough to the next crest which is another 1 M, so its 2M....

you can do the same thing if you go from trough to crest then the crest to trough. If you draw it out on paper you might be able to see it better, hope this helps.

 

[loreben]

2/3 is the right answer and after drawing it out on paper like you suggested it was clearer to be as to why the wavelength was 2m.

Thanks🙂

 

[cartman1980]

So 1m is between a crest and trough, and not between 2 crests or 2 troughs...

 

[rrmix]

So 1m is between a crest and trough, and not between 2 crests or 2 troughs...

It is 1 M to go from the highest point of the wave to the lowest point of the wave, which is half the wavelength