Posted by Johnson on .
A ruler is accurate when the temperature is 25°C. When the temperature drops to 16°C, the ruler shrinks and no longer measures distances accurately. However, the ruler can be made to read correctly if a force of magnitude 1.2 103 N is applied to each end so as to stretch it back to its original length. The ruler has a crosssectional area of 1.50 105 m2, and it is made from a material whose coefficient of linear expansion is 2.10 105 (C°)1. What is Young's modulus for the material from which the ruler is made?

Physics 
drwls,
Set the (negative) thermal expansion equal per unit length to the strain due to tension.
alpha*(delta T) = (F/A)/Y
Y = (F/A)/[(delta T)*alpha]
Y is Young's modulus
A is the cross sectional area, 1.5*10^5 m^2
delta T = 41 C
F = 1200 N
alpha = 2.1*10^5 C^1 is the coefficient of thermal expansion
Solve for Y 
Physics 
Johnson,
that's what I have been working and keep coming up with either two answers 9.29 or 9.29 * 10 ^10 and the computer is telling me its wrong I don't know what else to do. Maybe I'm computing the number wrong.

Physics 
drwls,
I also get 9.29*10^10 N/m^2. That is a typical value for a metal.