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Math Help - Value of h=48t-16t^2 when t = 2 and t = 2.5.

  1. #1
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    Value of h=48t-16t^2 when t = 2 and t = 2.5.

    The two questions are similar but I keep getting way different answers

    A water rocket is launched upwards with an initial velocity of 28 ft/sec. Its height H in feet after t seconds is given by h=48t-16t^2. Determine the height of the rocket after 2.5 secs after it has been launched.

    The second question is the same, but 2.0 secs after launch

    Thanks so much guys
    Last edited by mr fantastic; December 7th 2011 at 03:18 PM. Reason: Re-titled.
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  2. #2
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    Re: help with 2 word problems - factoring

    Quote Originally Posted by bashemgud View Post
    The two questions are similar but I keep getting way different answers

    A water rocket is launched upwards with an initial velocity of 28 ft/sec. Its height H in feet after t seconds is given by h=48t-16t^2. Determine the height of the rocket after 2.5 secs after it has been launched.

    The second question is the same, but 2.0 secs after launch

    Thanks so much guys
    Substitute t = 2.5 and t = 2 into h=48t-16t^2 and do the arithmetic.
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  3. #3
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    Re: Value of h=48t-16t^2 when t = 2 and t = 2.5.

    so 2.0 secs is 32feet and 2.5 is 20 feet?

    for some reason it seems backwards to me.
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  4. #4
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    Re: Value of h=48t-16t^2 when t = 2 and t = 2.5.

    This is because after 1.5 seconds, the rocket is descending.
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  5. #5
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    Re: Value of h=48t-16t^2 when t = 2 and t = 2.5.

    Quote Originally Posted by bashemgud View Post
    so 2.0 secs is 32feet and 2.5 is 20 feet?

    for some reason it seems backwards to me.
    Your answers are correct but your discomfort with them is concerning. I suggest you review parabolas and their graphs.
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  6. #6
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    Re: Value of h=48t-16t^2 when t = 2 and t = 2.5.

    Thanks everyone.
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