Cantilever BEAM !!! little problem. I have solved almost everything. 1. The problem statement, all variables and given/known data The link below has the problem: http://i52.tinypic.com/2r3bcdc.jpg 2. Relevant equations M = E*I(d^2*w/dx^2) slope = E*I (dw/dy) = integral of E*I(d^2*w/dx) + c1 deflection = E*I * (w) = double integral of E*I(d^2*w/dx) + c1x + c2 Bounding Condition: when x = 0 --> w = 0 and slope = 0 when x = L --> V = 0 and M = 0 Yb = ΣAY / ΣA I = Σ(I* + Ad^2)i 3. The attempt at a solution E*I(d^2*w/dx^2) = (-px^2/2) + (pLx) - (pL^2/2) E*I (dw/dy) = (-px^3/6) +(pLx^2/2) - (pL^3/6) + c1 (c1 = 0 using when x = 0, slope=0) w = (- p/(24*E*I)) * [x^4 - 4*L*x^3 + 6*L^2*x^2] + c2 (c2 = 0 using when x=0, w = 0) I then solved for the I knowing that Yb = 9. I had to transform everything to steel, using n = 30 / 10 = 3. The new dimensions for steel become 4" by 18" (which is the same) and for Al = (4+4)*3 = 24" by 18". Then i calculated the I, and got I = 13608 in^4. THE PROBLEM I HAVE IS THAT I DONT KNOW WHICH MODULUS OF ELASTIC TO USE FOR w = (- p/(24*E*I)) * [x^4 - 4*L*x^3 + 6*L^2*x^2] we know that p = 500, L = x = 20, I = 13609, E = ???