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Help with torque question

  1. Jan 25, 2009 #1
    1. The problem statement, all variables and given/known data

    The figure shows scale drawing of a pair of pliers being
    used to crack a nut, with an appropriately reduced centimeter grid.
    Warning: do not attempt this at home; it is bad manners. If the
    force required to crack the nut is 300 N, estimate the force required
    of the person's hand.( the pliers have a 10cm handle)

    2. Relevant equations

    3. The attempt at a solution
    I dont know how to start with this one.
  2. jcsd
  3. Jan 25, 2009 #2


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    Homework Helper

    Don't you have the equation?

    Figure the mechanical advantage from the hand side to the nut side?

    Plug in the numbers?
  4. Jan 25, 2009 #3
    If I use the equation i would need 3000N of force to break the nut. Thats way off. That cant be the right equation.
  5. Jan 25, 2009 #4


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    Homework Helper

    The mechanical advantage is what you need to know.

    How far from the pivot is the jaws holding the nut?

    You missed my edit in my first post.
  6. Jan 25, 2009 #5
    Whats the formula for MA that i could use?
  7. Jan 25, 2009 #6
    How do i get the input force if I dont know the MA and i only know the output force?
  8. Jan 25, 2009 #7


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    Homework Helper

    You don't need m*a.

    The hand exerts a force through the pivot to the jaws and the nut.

    On one side is the nut. The other your hand.

    The length away from the pivot your hand is divided by the length away from the pivot the nut is, is your mechanical advantage.

    If your hand is squeezing 10 cm from the pivot and the nut on the other side is 2 cm away, then that ratio 10/2 is the mechanical advantage.

    For my example only then 300N / 5 (the mechanical advantage is the force that needs to be applied.
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