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Calculating Force exerted on a skydiver when Parachute opens?

  1. Apr 14, 2004 #1
    Calculating Force exerted on a skydiver when Parachute opens??

    Ok. So i want to calculate the force in Newtons that is exerted on a skydiver when the parachute is deployed. I have the deceleration that the parachute causes, the velocity that the skydiver is going right as the parachute is deploying and the mass of the skydiver. How would I go about finding this?

    My followup question is: How would I find the impulse of this force? Is it just the force multiplied by the amount of time the skydiver experiences it for? Thanks!! :smile:
     
  2. jcsd
  3. Apr 14, 2004 #2
    I would use energies and momentum.

    First, the change in the skydiver's momentum is:

    [tex]Ft = \Delta P = m\Delta v = m(v_2 - v_1)[/tex]

    Second, the change in the skydiver's energies is:

    [tex]W_F = \Delta E_k + \Delta E_p[/tex]

    [tex]F\Delta h = \frac{1}{2}m(v_2^2 - v_1^2) + mg\Delta h[/tex]

    Now what you need to do is relate Δh to t (the time it takes the parachute to completely open) and solve the equations for F. I've assumed that the force exerted on the skydiver is constant throughout the parachute openning.
     
  4. Apr 14, 2004 #3
    Well, after reading your question again it seems you don't have to go through all that. If you already have the deceleration caused by the parachute, and the skydiver's mass... just multiply them to get the net force on the skydiver, and substract gravity to find the force exerted by the parachute. :smile:
     
  5. Apr 14, 2004 #4
    Hey, thats what I was thinking also. But I;m wondering if I should multiply the decleration by the mass of the parachute or the mass of the body? Since the parachute is the acting force would it be the parachute mass? Thanks!

    Also, any idea how to find Impulse? :redface:
     
  6. Apr 14, 2004 #5
    You should use the skydiver's mass, because you are working with the deceleration of the skydiver (it doesn't matter what object causes the force).

    Impluse equals change in momentum, so:
    J = ΔP
    FΔt = mΔv
    So you need to either find the change in velocity of the skydiver, or the amount of time the parachute exerts the force on the skydiver. I honestly can't see how you can find either of them, at least with the information that the problem provides. Are you not given any more data to work with? :redface:
     
  7. Apr 14, 2004 #6
    Hazzard,

    The answer depends on what you mean by "I have the deceleration that the parachute causes". Do you mean:

    Do you really mean:

    1) "I have the the deceleration that the parachute causes"

    Or do you mean:

    2) I have the the deceleration of the diver?

    If it's #2, just use that deceleration and the mass of the diver in Newton's 2nd law and add the force of gravity (mg).

    But if it's #1, it's not so easy, because the parachute isn't the only thing causing the diver to decelerate. There's air resistance to consider as well.

    Waht is the deceleration of the diver?
     
    Last edited: Apr 14, 2004
  8. Apr 14, 2004 #7
    I mounted an accelerometer on my helmet while jumping. I have the deceleration value that the head incurs because of the parachute opening. Thanks.
     
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