Question's on Sound

[pnoybballin]

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hey everyone I need some help with 2 questions from sound..

1) Which of the following frequencies moves fastest through water?

A. 200 Hz
B. 1000 Hz
C. 5000 Hz
D. They all move with the same velocity

The answer is D but isn't v = (lambda)f and thus a higher f = higher v?

2) By what factor would a string's tension need to change to increase it's fundamental frequency by 33.3%, given f is frequency, T is tension, p is density and L is length.

f = Square root of (T/p) / 2L

A. 3/4
B. Square root of (3/2)
C. 4/3
D. 16/9

The answer is D could someone please explain this one?

Thank you so much everyone.

 

[RogueUnicorn]

if you increase frequency you decrease wavelength, maintaining same velocity. under your logic, violet light would travel faster than red light etc, but obviously that's not the case

 

[Charles_Carmichael]

Yup, what bleargh says is true. All the sound waves would travel at the same velocity in a particular medium; if they have a high frequency, they'll have a lower wavelength and vice versa.

For your second question, the equation simplifies to:

f = sqrt(T)

This is because you don't really need to worry about the other variables; they remain constant. Now, the frequency increases by 1/3. What this means is that the frequency is now 3/3 + 1/3 = 4/3. Rememer to add this increase to the original amount, which is one. So, now, your setup looks like:

f = sqrt(T)
4/3 = sqrt(T)
T = 16/9

Hope this helps.