computing $L_2$ norm

Question

Let $x_i, i=1, \ldots, N$ are in $R$. Consider $\bar x=\frac 1N \sum_{i=1}^N x_i$. Let vector $y$ has component $x_i-\bar x, \quad i=1, \ldots, N$.

Compute the norm $\|y\|_2$.