How Do You Calculate the Tension and Elastic Properties of Suspended Wires?

[BadlyAddicted]

Homework Statement

Two wires each of 2.50m long, one of steel of diameter 1.0mm and the other of copper of diameter 0.56mm are suspended from two points in the same horizontal plane 200mm apart. The lower ends of the wires are fixed to the two ends of a uniform bar 200mm long and of weight 20.0N

A mass of 6.0kg is suspended from the center of the bar. The bar tilts at 0.8degrees to the horizontal. The young modulus of steel is greater than that of copper. Assume the wires remain vertical.

i) What is the tension in each wire?
ii) Calculate the extension of steel
iii) Determine the young modulus of the copper wire
v) Calculate the strain energy stored in the two wires.

The acceleration of free fall is 9.8ms^-2 and the Young modulus of steel is 2.0 * 10^11 Pa.

Homework Equations

The equations to be used are probably these (from my knowledge):
strain = extension/length
stress = tension/area
young modulus = stress/strain = FL/Ae

The Attempt at a Solution

i) [ 20 + (6 * 9.8) ] / 2= 39.4

If someone could work out ii and iii for me showing all the working i'd appreciate. i believe i can proceed from there

 

[member 553083]

with the information given.ii) Extension of steel = [ ( 20 + (6 * 9.8) ) / 2 ] * 0.01m / (2.50m)= 0.00796miii) Young Modulus of Copper = FL/Ae = [ ( 20 + (6 * 9.8) ) / 2 ] * 0.01m / (0.56mm * 0.00796m) = 2.37 * 10^11 Pa