Question

A football is kicked at ground level with a speed of 18.0 m/s at an angle of 31.0 degrees to the horizontal. How much later does it hit the ground?

Answer 1

Vy_initial= 18 * sin(31) since you want the Y component only

now we can use the following equation:
\[v _{final} = v _{initial} + a \times t\]
And if we set V_final to represent where the ball reaches a maximum height then we know V_final will be 0.

Therefore:
0 = [18 * sin(31)] + [(-9.8) * t] .... just solve for t

once you have t, you just need multiply it by 2 because the time you just solved in the equation above is only for half the trip (the time it took for the ball on its way up, not down)