Question

A football is kicked at ground level with a speed of 17.9m/s at an angle of 36.0∘ to the horizontal. How much later does it hit the ground?

Answer 1

just a vertical problem
Vi = 17.9 sin 36.0

h = 0 + Vi t - 4.9 t^2
0 = 0 + t (Vi - 4.9 t)
so it is at ground level at t = 0 of course
and
at t = Vi/4.9

Answer 2

Now divide your problems up into vertical problems and horizontal problems

if horizontal speed is u at start it is u to the finish
so
x = u t

if initial vertical speed is Vi
then
v = Vi - 9.81 t (remember v=0 at top)
h = Hi + Vi t - 4.9 t^2

Answer 3

in general if speed is s at A degrees above horizontal

u = s cos A

Vi = s sin A

Answer 4

Now you should be able to do them.