11) A metal wire of diameter 0.68 mm and natural length 1.5 m is fixed firmly to the ceiling at one end. When a 6.8 kg mass is hung from the free end, the wire extends by 2.8 mm.

Calculate:

a) the stress in the wire

B) the Young modulus of the material of the wire.

Rauhan Dec 2, 2017

#1**+1 **

FIRST find the VOLUME of the wire:

pi x r^2 x l = 5.45 x10^-7 m^3

THEN find its diameter given the NEW length of 1.5028 M

pi x r^2 x l = 5.45 x 10^-7 results in r =3.3968 x10^-4 m

then, as before Stress = F/A F= ma = 6.8(9.8) = 66.64 newtons

A= area = pi x r^2 where r is the 'new ' stretched r

Let me know what you come up with for an answer and we will continue..... ~EP

ElectricPavlov Dec 2, 2017

#2**+1 **

If you have the correct answer for stress (I got 1.83838 x 10^8 P )

then, (I had to look this one up !)

Young's Modulus = Stress / (\( \Delta \)L/ Lo) \(\Delta \)L = change in length = .0028 m Lo=1.5 m (given)

ElectricPavlov Dec 2, 2017