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Forces in a dynamic problem

  1. Sep 14, 2013 #1
    1. The problem statement, all variables and given/known data

    A 40kg person is falling at the speed of gravity, 9.8m/s^2. Wind resistance is not considered. On your free-body diagram, the direction they are falling (ground) is in the negative direction, hence gravity is causing an acceleration in the negative.

    2. Relevant equations

    F(gravity) = (40)(-9.8)
    F(gravity) = -392N

    3. The attempt at a solution

    I am simply curious when solving a problem such as this, would N be a -392N since it is traveling in the negative on the free-body diagram, or is it seen a magnitude and considered a positive number?
  2. jcsd
  3. Sep 14, 2013 #2
    Force is a vector therefore it has a direction. Also the direction of the movement of the object and the direction of the force do not have to me the same. For example a ball going up after you throw it moves up but the force acting on it is downward.
  4. Sep 14, 2013 #3
    Thank you.
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