It is a 2 meters long vacuum cannon.

P = Atmospherics pressure = 101325 Pascal

r = 0.02 meters

A = (pi)(r)^2

F = PA

F = (101325)(3.14 X 0.04) = 12732.8750

W = Fd = (12732.8750)(2) = 25465.75

W = (1/2)(m)(V)^2

V = square root((2 X 25465.75)/0.04) = 1128

V = 1128 m/s

Redo your calcs, this time square r, F=(101325)(3.14x0.02x0.02)=127.328

W=127.328x2=254.657

V=sqrt((2x254.657)/0.04)=112.83 m/s I think

Tom