SOLUTION: a stone is thrown vertically upwards at a speed of 24 m/s. its height h meters after t seconds is given approximately by the formula h=24t-5t squared. Use this formula to find whe

Question 281548: a stone is thrown vertically upwards at a speed of 24 m/s. its height h meters after t seconds is given approximately by the formula h=24t-5t squared. Use this formula to find when the stone is 27 meters up, and explain the double answer.
Answer by Alan3354(69443) (Show Source): You can put this solution on YOUR website!
a stone is thrown vertically upwards at a speed of 24 m/s. its height h meters after t seconds is given approximately by the formula h=24t-5t squared. Use this formula to find when the stone is 27 meters up, and explain the double answer.
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h(t) = 24t - 5t^2
-5t^2 + 24t - 27 = 0

Solved by pluggable solver: SOLVE quadratic equation (work shown, graph etc)

Quadratic equation (in our case ) has the following solutons:

For these solutions to exist, the discriminant should not be a negative number.

First, we need to compute the discriminant : .

Discriminant d=36 is greater than zero. That means that there are two solutions: .

Quadratic expression can be factored:

Again, the answer is: 1.8, 3. Here's your graph:

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at t=1.8 seconds it's at 27 meters and rising.
at t=2.4 seconds it's at its max height and starts to fall.
at t=3 seconds it's at 27 meters and falling.

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