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.
a) the stress in the wire
B) the Young modulus of the material of the wire.
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
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)