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Homework Help: Resultant Force

  1. Aug 7, 2011 #1
    Hi guys, please help me with this problem. thanks

    A 75 kg sky-diver in free fall is subjected to a crosswind exerting a force of 60 Newton and to a vertical air resistance force of 100 Newton. Describe the resultant force acting on the skydiver.

    I used the formula to calculate the resultant force:

    Resultant Force (square) = 60 (square ) + 100 (square)

    But this formula gave me the answer 117 Newtons

    Answer given in my text book is:

    638.6 Newton at an angle of 5.4 degrees to vertical.
    Last edited: Aug 7, 2011
  2. jcsd
  3. Aug 7, 2011 #2
    Please, follow the pattern provided in the rules section. We cannot provide you any help if you don't post us your attempt to solve the problem.
  4. Aug 7, 2011 #3
    This was my attempt. Couldnt think of any other solution to the problem.
  5. Aug 7, 2011 #4
    I'm so sorry, I didn't see it :blushing::blushing::blushing::blushing::blushing::blushing::blushing:

    Have you considered the sky-driver weight?
  6. Aug 8, 2011 #5
    I meant to say that I had revised my question, I have mentioned the formula which I have used as well. Please check.

  7. Aug 8, 2011 #6


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    Take note of DiracRules's suggestion.

    The cross wind acts sideways.
    The air resistance acts UP.
    Is the sky-diver accelerating UP?
  8. Aug 8, 2011 #7
    The sky diver is in FREE FALL motion, obviously accelerating downwards, I'm still getting my answer wrong though !!

  9. Aug 8, 2011 #8


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    You need to get the resultant vertical force and then use that in addition to the cross wind to get the overall resultant.

    Write down the equation for the resultant vertical force.
  10. Aug 8, 2011 #9
    And how do you describe the fact that he is free falling in terms of forces?
  11. Aug 8, 2011 #10


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    Things only travel in the direction of the force.

    When the skydiver left the plane, if the cross wind provided the only force, he would have gone sideways.
    He didn't he went down; eventually so fast that an upward force of air resistance developed.

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