L = 25.3 (slider from 0 to 50, step 0.1)
f(x) = -10 / L^(3) * x^(3) + 15 / L^(2) * x^(2)
A = (0, 0)
Aire = Integral(f, 0, L)
g = Function(f, 0, L)
volume: Aire * 90
masse: volume * 7.1 / 10^(4)