How to extract coordiante values from intersections in one \begin{axis} environment to use in a second \begin{axis}.. environment in pgfplots

I would like to plot two graphs, side by side, in two separate \begin{axis}...\end{axis} environments using pgfplots. In one graph I want to plot the n curves y1=x^2, y2=2x^2,..., yn=nx^2. I then want to calculate the intersections of yi (i=1,..,n) and y=5, call this set {(xi,zi)}, and on the SECOND graph, produce a scatter plot of the data (zi,i).

I realise that the usual method is to post example TeX, but I really have no idea where to start with this and I think the problem is simple enough.

Many thanks.