Suppose that $f$ is continuous and $|f(x)|<1$ for all $x$ in $[a,b]$. Does $[f(t)]^n$ converge uniformly to $0$?
Is it a no? Because if I have $x^n$ then at $x$ very close to $1$ it takes very long to converge to $0$, so we can't find an $N$ such that with all $n > N$, $x^n$ converges to $0$.
HINT: The function $|f|$ is continuous, so it attains its maximum at some point $c\in[a,b]$. Clearly $0\le |f(c)|<1$. What can you say about $|f(x)|^n$ in terms of $|f(c)|$?