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A ball is thrown from an initial height of 3 meters with an initial upward velocity of 20m/s. The ball's height (in meters) after seconds is given by the following h=3+20t-5t^2. Find all values of for which the ball's height is 13 meters.

Aug 7, 2021

#1
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h = 13 meters

13 = -5t^2 + 20t + 3

-5t^2 + 20t -10 = 0           we can simplify this a bit by dividing through by -5

t^2 -4t +2 = 0         Now use the quadratic formula to find the t values (two of them) ...one will be for the ball on the way UP

the larger one will be for whe the ball is coming DOWN .

a = 1    b= -4    c = 2

$$t = {-(-4) \pm \sqrt{(-4)^2-4(1)(2)} \over 2(1)}$$     I will let you finish.....

Aug 7, 2021