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Homework Help: What value of the velocity should I insert in the equation?

  1. Jun 9, 2009 #1

    My problem is very simple... but yet it rises some doubt. I am calculating how long a projectile goes taking into account air drag. For the displacement I have the following formula:


    where k is the air drag coefficient

    I know that this formula already includes both components of the velocity, thus it should give the correct displacement.
    The equation states that my initial velocity is: 31.1m/s
    The X component of the velocity is: 15.55m/s.

    Which value of the velocity should i insert on the equation?

    I have done the calculations with both and the results differed by very little, hence my confusion.

    Appreciate the help, thanks.

  2. jcsd
  3. Jun 9, 2009 #2


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    Homework Helper

    Which equation of motion did you solve to get that formula for the displacement?
  4. Jun 9, 2009 #3
  5. Jun 9, 2009 #4


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    Homework Helper

    You're missing an m in there I think and +g should be -g. Since you have a g in that particular equation of motion the v and x you calculate will be in the y-direction. Therefore you need to calculate the y-component of the initial velocity.
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