Question 287437: Hello all, I have an interesting problem here that I'm not sure how to solve correctly.
The problem involves a rocket being shot into the air where H = Height of the rocket in the given equation. I need to solve for certain conditions etc. but dont know how to write out the equations to rearrange.
Original Equation is: H= -5t^2 + 20t + 15 where H = Height and t = Time.
a) What is the maximum height reached by the rocket, at what time does this occur?
b) Find the time(s) when the rocket is 20 metres above the ground.
c) How long will it take for the rocket to hit the ground?
Help with any of the above will be most appreciated.
Thnaks, -Nick.
Answer by scott8148(6628)   (Show Source):
You can put this solution on YOUR website! the equation is a quadratic in t
the graph is a downward opening parabola
a) H-max is at the vertex of the parabola, which is on the axis of symmetry
___ general equation for axis of symmetry ___ x = -b / (2a)
b) plug in 20 for H and use the quadratic formula to find the values of t, one going up and one coming down
c) same as b) except H=0 ___ only the positive value of t is applicable
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