Maximum take off speed of a F-35B lightning with VTOL?

I am really interested in the F-35 jet and wanted to know what the maximum take off velocity of the F-35B is (it starts vertically). I calculated it by using E=m*g*h but with the sources i got, that would mean that the jet can only increase its height by 71cm/s, which in my opinion is really really slow. Can you please help me out and tell me if this could be a reasonable velocity or tell me the real value.