Posted by **Melissa** on Monday, October 17, 2011 at 10:28pm.

The height of a ball thrown vertically upward from a rooftop is modelled by y=-5t^2+20t+50 , where h(t) is the ball's height above the ground , in meters , at time t seconds after the throw

a) Determine the max height of the ball

b) how long does it take for the ball to reach its max height

c) How high is the rooftop

- Math( help please ! ) -
**Steve**, Tuesday, October 18, 2011 at 4:39am
y = 5(10 + 4t - t^2)

max height achieved where t = -b/2a = 2

y(2) = -5(4) + 20(2) + 50 = 70

as above, when t=2

The rooftop is the ball's initial height. That is, when t=0. So, 50 ft.

- Math( help please ! ) -
**Melissa**, Tuesday, October 18, 2011 at 8:37am
thank you so much

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