A player kicks a football from ground level with a velocity of magnitude 31.0 m/s at an angle of 30.0 degrees above the horizontal. What is its maximum height?

Answer 1

The vertical component of velocity is: Vy = 31 sin 30 = 15.5 m/s
That is what determines the maximum height, H.

The maximum height is given by
sqrt(2 g H) = Vy
H = (Vy)^2/(2g)

Answer 2

12.0m