Physics (quick check)
posted by Mo .
A football is kicked at ground level with a speed of 20.8m/s at an angle of 23.3 degress to the horizontal. How much later, in seconds, does it hit the ground?
Tf =(20.8m/s x Sin 23.3)/9.80m/s^2
=0.839s
this doesn't sound right to me

h(t)=h(0)+vvt1/2 g t^2
0=0+20.8sin23.3 t  4.9t^2
t=0, t=20.8sin23.3/4.9
so your denominator is wrong.