# Homework Help: Thermal Force Physics

1. Oct 24, 2009

### Punkyc7

1. The problem statement, all variables and given/known data
Suppose the ends of a 20-m-long steel beam are rigidly clamped at 0°C to prevent expansion. The rail has a cross-sectional area of 30 cm^2. What force does the beam exert when it is heated to 40°C? ( αsteel = 1.1 × 10−5/C°, Ysteel = 2.0 × 1011 N/m2).

2. Relevant equations

delta L =alpha Li delta T

3. The attempt at a solution
I solve for the new lenght and get 20.0088m. I dont know what Ysteel is used for or were to start after finding the new lenght.

Last edited: Oct 24, 2009
2. Oct 24, 2009

### Punkyc7

The answer is one of these if that helps
a. 2.6 × 105 N
b. 5.6 × 104 N
c. 1.3 × 103 N
d. 6.5 × 102 N
e. 2.5 × 102 N

3. Oct 24, 2009

### Mapes

Do you know what the Young's elastic modulus Y signifies and how to work with it? If so, how much stress (and then, how much force) is required to compress the length back to 20 m?

4. Oct 24, 2009

### Punkyc7

no i havent seen it before, what is the equation?

5. Oct 24, 2009

### Mapes

You might want to read http://en.wikipedia.org/wiki/Young%27s_modulus" [Broken].

Last edited by a moderator: May 4, 2017
6. Oct 24, 2009

### Punkyc7

thanks i got it now