F.4 Maths

h = 30t - 5t^2
h = - 5(t^2 - 6t)
h = -5(t^2 - 6t +9 +9)
h = -5(t - 3)^2 + 45
∴ t =3 seconds(the ball attains its max height)
and the max. height be 45 m.
the half of its max height = 45/2
put h = 45/2 into the equation
h = 30t - 5t^2
∴ 45/2 = 30t - 5t^2
5t^2 - 30t + 22.5 = 0
t = 5.12 or t = 0.879

the values of t = 5.12 s or 0.879 s when the ball...