v(t)

a(t)

v(x) = ((-0.5 * x^(2)) + (20 * x)) / 3.6
v0(x) = If[0 ≤ x ≤ 20, v(x)]
a(t) = v'(t)
a0(x) = If[0 ≤ x ≤ 20, v'(x)]
b = Integral(a, 0, 20)