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Finding max force at bottom of a 2.8m decline swinging on a vine?

  1. Feb 25, 2013 #1
    Tarzan, who weighs 662 N, swings from a cliff at the end of a convenient vine that is 21 m long (see the figure). From the top of the cliff to the bottom of the swing, he descends by 2.8 m. The vine will break if the force on it exceeds 1340 N. What would the greatest force on the vine be during the swing?


    PE=mgh
    KE=1/2mv2


    Not sure which equation to use here...

    Thank you!
     
  2. jcsd
  3. Feb 25, 2013 #2

    tms

    User Avatar

    You're looking for the tension in the vine. Draw a diagram showing all the forces and proceed from there.
     
  4. Feb 26, 2013 #3
    Greatest force is at the largest acceleration.

    [itex]F=ma[/itex]
    [itex]a=\frac{V^2}{r}[/itex]
    [itex]F=\frac{mV^2}{r}[/itex]

    ∴ Greatest acceleration is at the greatest velocity.

    You will need both ##P.E=mgh## and ##K.E=\frac{1}{2}mV^2##
    ##P.E## to find the energy gained and you will need to rearrange ##K.E## to find the velocity at that energy.

    If he decends 2.8m ##h=2.8##

    That is the force due to swinging, you must also add on gravity [itex]F=mg[/itex]
     
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