What is the air speed after passing through a nozzle?

[_greg]

If a circular pipe with diameter 4ft has an airspeed of 100mph which then funnels through an orface(sp?) with diameter 2ft, what is is the air speed after the air passes though the hole?
Any help would be very much appreciated. I am completely lost...

 

[rwooduk]

Take a look at this, I think it's relevant:

http://en.wikipedia.org/wiki/Incompressible_flow