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Finding net torque problem

  1. Jul 31, 2016 #1
    1. The problem statement, all variables and given/known data
    Find the net torque on the wheel in the figure below about the axle through O, taking a = 13.0 cm and b = 31.0 cm. (Assume that the positive direction is counterclockwise.)
    pic: https://fbcdn-sphotos-c-a.akamaihd...._=1470130918_26fa32f17821823200ba75439cef0a52



    2. Relevant equations τ=f⋅d


    3. The attempt at a solution
    just sum all for torque, I thought you could just go
    τ1=9.0N ⋅ 0.31m = 2.79 n⋅m
    τ2=10.0N⋅0.31 = 3.1 N⋅ m
    but the torque component with the angle shown, I calculated it the same and then summed all the values of torque together, and it said it was wrong, so im assuming that you have to add something like a cosine or sine into that component because it isnt in a horizontal or vertical direction but 150° below the horizontal (positive x axis) any tips on how to solve this,????
     
  2. jcsd
  3. Jul 31, 2016 #2

    Orodruin

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    This does not actually show us what you did. Please specify the values you put in and the result you got.
     
  4. Jul 31, 2016 #3
    i dont understand how it doesnt show what i did? i completely explained what i did. the two net torques i gave how i calculated them and got 2.79 N.m and 3.1 N.m and said i did the same for the third component so obviously following that i went 12.0N x 0.13m which gave me 1.56 N.m, then i said i summed all my values for torque together, thus 2.79+3.1+1.56 which equals 7.45N.m but that value was incorrect. Does that explain it anymore or was there something else you need to know??
     
  5. Jul 31, 2016 #4

    haruspex

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    No, you left out this initially:
    Think about directions (more precisely, "sense").
     
  6. Jul 31, 2016 #5

    Orodruin

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    No you did not, you left out a crucial part, your computation of the last contribution and the final result. Haruspex has already given you a good hint. Try to interpret it and ask again if you still cannot work it out.
     
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