# Physics- waves and energy

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#1
Hi
i need help with this question why do we use the circumference of a circle over the area of a circle? Also once I calculated the energy how I know whether or not the string breaks?
The string is fixed at one end and wrapped around a tuning peg of radius 3.0 mm at the
other. The tuning peg needs to be turned through 3 complete rotations to increase the
tension in the string from 0 to 70 N in part (c).
Discuss, by estimating the energy stored in the string, whether there is a significant risk to
the guitar player when the string breaks.
0
1 month ago
#2
You use the circumference because you have to calculate the extension of the string. The cross-sectional area of the tuning peg doesn't feature in any of the calculations.
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#3
(Original post by Sinnoh)
You use the circumference because you have to calculate the extension of the string. The cross-sectional area of the tuning peg doesn't feature in any of the calculations.
right- but my question is why or is this a general rule?
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1 month ago
#4
(Original post by Sclaremonths)
right- but my question is why or is this a general rule?
The question is about energy stored in the spring, energy stored is proportional to extension squared, to work out the extension when it's wrapped around a circle you would use the circumference of the circle and not the area. If it were wrapped around a pentagon you'd use the perimeter of that.
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#5
(Original post by Sinnoh)
The question is about energy stored in the spring, energy stored is proportional to extension squared, to work out the extension when it's wrapped around a circle you would use the circumference of the circle and not the area. If it were wrapped around a pentagon you'd use the perimeter of that.
okay thank you!
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