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Math Help - Finding the time it takes to hit the ground

  1. #1
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    Finding the time it takes to hit the ground

    The question reads

    The ball is tossed up in the air from a tower 50m above the ground. If the ball has an inital velocity of 30m/s, how long will it take to hit the ground if a = -9.8m/s^2.

    Now ive got my velocity function v = -10t +30, my height function h = -5t^2 +30t + 50, how can I find the total time?

    Thank You!
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  2. #2
    Super Member craig's Avatar
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    First let us see what in formation we have:

    s - Displacement - 50 metres
    u - Initial velocity - 30m/s
    v - Final velocity - N/A
    a - Acceleration - 9.8m/s
    t - Time - ?

    We will take all values as downward, that is why we have acceleration as a positive value.

    From the above information you should notice that we can use the following formula

    s = ut + \frac{1}{2}at^2

    Subbing in our values gives us,

    50 = 30t + 4.9t^2

    Which is just a normal quadratic.

    Hope this helps

    Craig
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  3. #3
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    Quote Originally Posted by Meeklo Braca View Post
    The question reads

    The ball is tossed up in the air from a tower 50m above the ground. If the ball has an inital velocity of 30m/s, how long will it take to hit the ground if a = -9.8m/s^2.

    Now ive got my velocity function v = -10t +30, my height function h = -5t^2 +30t + 50, how can I find the total time?

    Thank You!
    h = -4.9t^2 + 30t + 50

    set h = 0 and use the quadratic formula to solve for t.
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