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Question 144379: I have no idea how to do this question.
A projectile so shot from a platform 100 feet above the ground with an intial velocity of 39 feet per second. It's height above the ground in t seconds is given by the quadratic polynomial: h=-16t+39t+100
Graph the projectiles height from t=0 until it hits the ground, indicate the maximum height reached and the number of seconds passed until it strikes the ground on the graph.
The graph is just and L shape.Y axis = height and the x axis = t in seconds.
Any help would be great.
Found 2 solutions by ankor@dixie-net.com, vleith:
Answer by ankor@dixie-net.com(22740)   (Show Source):
You can put this solution on YOUR website! A projectile so shot from a platform 100 feet above the ground with an initial velocity of 39 feet per second. It's height above the ground in t seconds is given by the quadratic polynomial: h=-16t+39t+100
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I think the equation should be: h = -16t^2 + 39t + 100
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Graph the projectiles height from t=0 until it hits the ground, indicate the maximum height reached and the number of seconds passed until it strikes the ground on the graph.
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Graph the equation where h = y and t = x
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On a graphing calc; enter -16x^2+39x+100, scale -2, +6, -10, +150
Should look like this:
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If you have to graph on paper, use the same scale and substitute values for x
0, .5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, and find y for each, plot
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It should look about the same
You can see it will strike the ground in 4 sec, Max height is about 125 ft at about 1.25 sec
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You can find the actual max by finding the vertex of he given equation.
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Did this make sense to you? Any questions?
Answer by vleith(2983)  (Show Source):
You can put this solution on YOUR website! Given:  you missed the t^2
To plot the graph, you realize that since the equation is quadratic, the shape is a parabola. You are asked to find two points. I think you need to plot 4 points to draw a 'good graph' for this one.
Point 1 is the starting point. You are told that at time=0, the height is 100. (0,100)
Now find these three other points.
Find the other point where the height is 100. The projectile goes up, so it will come down.
To find that other point, replace h with 100 and solve
t = 0, t= 39/16 (you see that point 1 is one of these. Point 3 the other one
(39/16, 100)
Now find the point at the time halfway between points 1 and 3. That time is
 =  . Plug that in for t and see what h is. Use that as point 2
The last point is the poiint where the projectile hits the ground. At that point, h =0.
Use the quadratic equation with a=(-16), b=39 and c=100 to find the positive time. Plot that as point 4 (t,0).
Now draw the curve.
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