Answer:
H = V t - 1/2 g t^2 V =vertical speed up and g is directed downwards
40 = 30 t - 5 t^2
8 = 6 t - t^2 divide by 5
t^2 - 6 t + 8 = 0
[6 +- (36 - 32)^1/2 ] / 2 = 2 or 4
Check (4 will mean the ball has reached max height and is moving down)
H = 30 * 4 - 5 * 16 = 120 - 80 = 40 m
2 of course will be the correct answer (6 - 2) / 2 = 2
H = 30 * 2 - 5 * 4 = 40 m
