zaid asked in Science & MathematicsPhysics · 5 years ago

Physics Static Equilibrium Problem force involved in standing tiptoe?

Update:

this is the Q

http://store2.up-00.com/2015-01/142066132351.jpg

i hope to get the answer and what did you did to get that result

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  • 5 years ago
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    The (2) eqations for statics

    Sum of the forces in any direction = 0

    Sum of the moments about any point = 0

    These (2) equations are really about all you need for any statics problem.

    Start with a moment balance about F3. The reason we do that is because the lever arm for F3 about F3 is 0 and we can eliminate that variable.

    Sum of the moments about F3 (CCW is +) = 0

    0 = F2*r3 - F1*(r1+r3)

    Solve for F2

    F2 = F1*(r1+r3)/r3

    Plug in numbers

    F2 = 784 N * (12 + 6 cm) / 6 cm = 2352 N

    Now do a force balance

    Sum of the vertical forces (up is positive) = 0

    0 = F1 - F2 + F3

    F3 = F2 - F1

    Plug in numbers

    F3 = 2352 N - 784 N = 1568 N

    Note: You could have done the moments about F2 to start with, but the answers would still be the same.... I checked.

    Hope I helped explain it.

    • ...Show all comments
    • civil_av8r
      Lv 7
      5 years agoReport

      F1*r1 = F3*r3 comes from doing a moment balance about F2. F1 spins clockwise, F3 spins CCW about F2.

      0 = F3*r3 - F1*r1
      F3*r3 = F1*r1

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