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Thread: Parabolas :)

  1. #1
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    Exclamation Parabolas :)

    Hello once again. I am having difficulties in understanding how to calculate these two questions regarding to a ball being thrown where its maximum height is at (2,144). The explanation and two questions are in the pictures below. Parabolas :)-screen-shot-2018-10-08-6.38.52-pm.png Parabolas :)-screen-shot-2018-10-08-6.39.17-pm.pngParabolas :)-screen-shot-2018-10-08-6.39.21-pm.png
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  2. #2
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    Re: Parabolas :)

    For (d) set the equation for the altitude of the ball equal to 84, and solve for 't.' Use the quadratic equation, and you'll get two values for 't' - the first is the time when the ball passes through the 84-meter level on its way up, and the second is when it passes the 84-meter level on its way down

    For (e) do the same, but set 'h' = 80. You should get one value for 't' equal to 0 (cause it's at 80 at the start), and the second value will be when it passes the 80-meter level on its way down. You will also need to find the value of 't' when 'h' = 0 (i.e., when the ball hits the ground). Once you have these values of 't' you can determine the required ratio.

    By the way, I know the problem states that the formula they provided is for the ball's height in meters, but whoever wrote the problem actually probably meant feet. That's because the basic motion of a projectile is h = (1/2)gt^2+v_0t+h_0, where 'g' is acceleration due to gravity, 'v_0' is the initial upward velocity of the projectile, and h_0 is its initial height. The value for 'g' near the Earth's surface is either -32 ft/s^2 or -9.8 m/s^2. So the fact that the formula they provided uses (1/2)g = -16 tells me that they intended the problem to be in feet, not meters.
    Last edited by ChipB; Oct 8th 2018 at 07:33 AM.
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