A water balloon is catapulted into the air from the top of a building. The height h(t), in meters, of a balloon after t seconds is h(t) = -5t(exponent 2) + 30t + 10. When will the balloon reach a height of 30m?
h(t) = 30
30 = -5t(exponent 2) + 30t + 10
30 = -5(t(exponent 2) - 6t -2)
I'm stuck here.
normally we'd find two numbers that add to the middle number (-6) and multiply to the last number (-2).
Help pleaseeeeee?
2007-11-18 10:24:52 · 5 answers · asked by Bo 3 in Science & Mathematics ➔ Mathematics
Just write it as -5t^2 + 30t + 10 = 30 , then write as
-5t^2 + 30t -20 = 0
Now use the quadratic equation to solve for t. You will get two answers. One is when it crosses 30 meters going up and the other when 30 meters are crossed going down.
If you don't know the quadratic equation - look it up.
2007-11-18 10:29:55 · answer #1 · answered by rscanner 6 · 0⤊ 0⤋
the quadratic equation is -b+(or)- the square root of b^-4*a*c all of that divided by 2*a. If you set it up as 30=-5t^2+30t+40 then set that = to zero and get 5t^2+30t+40=0 a=5 b=30 c=40
2007-11-18 10:36:39 · answer #2 · answered by Sefjoe 2 · 0⤊ 0⤋
you have to move the 30 to the other side first...
-5t^2 + 30t + 10 = 30
-5t^2 + 30t - 20 = 0
t^2 -6t + 4 = 0
use the quad eq to solve...
t = (6 +/- 2sqrt(5))/2
= 10.47, 1.53
2007-11-18 10:39:54 · answer #3 · answered by norman 7 · 0⤊ 0⤋
you have to get one side equal to zero before you do that. so...
30=-5t^2+30t+10
0=-5t^2+30t-20
0=-5(t^2-6t+4)
-5 is one answer, but to find the other answers, use the quadratic formula I guess.
2007-11-18 10:38:29 · answer #4 · answered by Mogget 2 · 0⤊ 1⤋