In a chase scene, a movie stuntman runs horizontally off the flat roof of one building and lands on another roof 2.0 m lower. If the gap between the buildings is 4.8 m wide, how fast must he run to cross the gap?

Answer 1

4.8 = u t
what is t, the time airborne?
2 = 4.9 t^2
so
t = sqrt(.408) = .639 second
so
u = 4.8/.639
= 7.51 m/s

Answer 2

where does the 4.9 come from