LetsFetz,
V2 is calculated as 1.2 x stall speed in takeoff configuration. At this speed the A/C should be able to maintain a safe rate of climb with one engine inop. This will vary with loading, temperature, pressure, etc.
35 feet is the minimum obstacle clearance required along the runway extended centerline (clearway) until reaching 1500ft.
Nothing to do with ground effect, as quid says.
I have to admit I never heard of an 50ft requirement. Is this a JAA/European reg.?
I never came across it in the FAA regs.