One end of a piano wire is wrapped around a cylindrical tuning peg and the other

Question

One end of a piano wire is wrapped around a cylindrical tuning peg and the other end is fixed in place. The tuning peg is turned so as to stretch the wire. The piano wire is made from steel (Y = 2.0x1011 N/m2). It has a radius of 0.85 mm and an unstrained length of 0.85 m. The radius of the tuning peg is 1.5 mm. Initially, there is no tension in the wire, but when the tuning peg is turned, tension develops. Find the tension in the wire when the tuning peg is turned through two revolutions.

F= Unit: N

Explanation / Answer

r = 0.85 mm , Y =2*10^11 N/m^2, L = 0.85 m

R = 1.5mm

strain = change in length/original length

= 2 turns of peg/L = 4*3.14*1.5*0.001/0.85

strain = 0.022

stree = F/A = Y*strain

F/(3.14*0.85*0.85*10^-6) = 2*10^11*0.022

F = 9982 N

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