# Find the maximum bending moment

1. Jul 30, 2009

### SteveMckenna

The bending moment, M, at position x meters from the end of a simply supported beam of length l meters carrying a uniformly distributed load of wkN m^-1 is given by:

M = w/2 l (l-x) - w/2 (l-x)^2

Show, using the above expression, that the maximum bending moment occurs at the mid-point of the beam and determine its value in terms of w and l.

I know that the max bending moment will occur at the root of the equation: d/dx M(x) = 0
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Jul 30, 2009

### Staff: Mentor

Sounds good to me. Go for it!
You need to make some sort of attempt before anyone here will help you out. The function you're working can be differentiated fairly easily.

3. Jul 31, 2009

### SteveMckenna

I believe that dM/dx = wl/2 - w(l-x) thus far!

Is this correct before I continue?

4. Jul 31, 2009

### Staff: Mentor

Your signs are wrong. For example, d/dx(w/2 * l(l - x)) = -w/2 * l