SOLUTION: If a stone is tossed from the top of a 310 meter building, the height of the stone as a function of time is given by h(t) = -9.8t^2 – 10t + 310, where t is in seconds, and height

Algebra ->  Customizable Word Problem Solvers  -> Travel -> SOLUTION: If a stone is tossed from the top of a 310 meter building, the height of the stone as a function of time is given by h(t) = -9.8t^2 – 10t + 310, where t is in seconds, and height       Log On

Ad: Over 600 Algebra Word Problems at edhelper.com


   



Question 387214: If a stone is tossed from the top of a 310 meter building, the height of the stone as a function of time is given by h(t) = -9.8t^2 – 10t + 310, where t is in seconds, and height is in meters. After how many seconds will the stone hit the ground? Round to the nearest hundredth’s place; include units in your answer.
Answer by nerdybill(7384) About Me  (Show Source):
You can put this solution on YOUR website!
h(t) = -9.8t^2 – 10t + 310
Set h(t) to zero (since when height = 0, it'll hit the ground):
0 = -9.8t^2 – 10t + 310
since we can't factor, we apply the "quadratic formula". Doing so yields:
x = {-6.16, 5.14}
We can toss out the negative solution leaving:
x = 5.14 seconds
.
Details of quadratic follows:
Solved by pluggable solver: SOLVE quadratic equation with variable
Quadratic equation ax%5E2%2Bbx%2Bc=0 (in our case -9.8x%5E2%2B-10x%2B310+=+0) has the following solutons:

x%5B12%5D+=+%28b%2B-sqrt%28+b%5E2-4ac+%29%29%2F2%5Ca

For these solutions to exist, the discriminant b%5E2-4ac should not be a negative number.

First, we need to compute the discriminant b%5E2-4ac: b%5E2-4ac=%28-10%29%5E2-4%2A-9.8%2A310=12252.

Discriminant d=12252 is greater than zero. That means that there are two solutions: +x%5B12%5D+=+%28--10%2B-sqrt%28+12252+%29%29%2F2%5Ca.

x%5B1%5D+=+%28-%28-10%29%2Bsqrt%28+12252+%29%29%2F2%5C-9.8+=+-6.15758942939662
x%5B2%5D+=+%28-%28-10%29-sqrt%28+12252+%29%29%2F2%5C-9.8+=+5.13718126613131

Quadratic expression -9.8x%5E2%2B-10x%2B310 can be factored:
-9.8x%5E2%2B-10x%2B310+=+-9.8%28x--6.15758942939662%29%2A%28x-5.13718126613131%29
Again, the answer is: -6.15758942939662, 5.13718126613131. Here's your graph:
graph%28+500%2C+500%2C+-10%2C+10%2C+-20%2C+20%2C+-9.8%2Ax%5E2%2B-10%2Ax%2B310+%29