Posted by **A.J.** on Saturday, November 21, 2009 at 5:08pm.

Please help if you can.

If a ball is shot projected straight upward at a rate of 64 feet per second from a rooftop, 80 feet above ground level, the height of feet above ground is modeled by the equation,

h(t)=-16t^2+64t+80

Find h(0), h(1),h(2)

Use the zero-factor property to determine how many seconds it will take for the ball to reach the ground? (What value of t makes h(t)=0)

- Math -
**Reiny**, Saturday, November 21, 2009 at 7:39pm
I will do one of them, you do the rest following my method, ok?

f(1) = -16(1)^2 + 64(1) + 80

= -16 + 64 + 80

= 128

when h = 0

-16t^2+64t+80 = 0

divide by -16

t^2 - 4t - 5 = 0

(t-5)(t+1) = 0

so t=5 or t=-1

clearly t > 0 ,so after 5 seconds it will reach the ground.

- Math -
**A.J.**, Saturday, November 21, 2009 at 8:00pm
Thank you so much. You really helped me understand. I can definitely finish the rest.

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