Integral not being computed

I want to compute the integral of normDf between a and b. What am I doing wrong?

This is my code

syms t
assume(t, "real")

f1 = 3*t-t*t*t;
f2 = 3*t*t;
f = [f1, f2]

f = 

df = diff(f, t)

df = 

a = 0;
b = 1;
normDf = sqrt(df(1)*df(1)+df(2)*df(2))

normDf = 

int(normDf, t, a, b)

ans = 

Answer 1

[Paul]

Simplify normDf before applying int(). Don't know why int() doesn't do this on its own

syms t
assume(t, "real")
f1 = 3*t-t*t*t;
f2 = 3*t*t;
f = [f1, f2];
df = diff(f, t);
a = 0;
b = 1;
normDf = sqrt(df(1)*df(1)+df(2)*df(2))

normDf = 

normDf = simplify(normDf)

normDf = 

int(normDf, t, a, b)

ans = 

4

Answer 2

[David Hill]

use vpaintegral

syms t
assume(t, "real")
f1 = 3*t-t*t*t;
f2 = 3*t*t;
f = [f1, f2];
df = diff(f, t);
a = 0;
b = 1;
normDf = sqrt(df(1)*df(1)+df(2)*df(2));
vpaintegral(3*(4*t^2 + (3*t^2 - 3)^2/9)^(1/2), t, a, b)