Chris threw a ball into the air vertically. The height of the ball above the ground can be modeled by the equation h(t)=-16t^2+30t+4 where h is the height in feet and t is the time in seconds.

Question

When will the ball hit the ground? Show your work/thinking.

Answer 1

h(t) = -16t^2 +30t + 4 = 0

-8t^2 + 15t +2 = 0

8t^2 -15t -2 = 0

factor

(8t+1)(t-2) = 0

t= 2 seconds or -1/8 of a second

ignore the negative solution

or use the quadratic formula if you don't figure out the factors

Answer 2

Erich,

You are being asked to find when "height" = 0

Can you factor the given parabola or "complete the square " and sketch it? If so, you can easily see what value makes h(t) = 0

Hope this helps--Andrew F.