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Homework Help: Question on torques. quick one.

  1. May 7, 2016 #1
    1. The problem statement, all variables and given/known data
    Untitled 3.jpg

    2. Relevant equations
    ok, I thought that the torque from the mass 'm' would be equal to torque from mass 'M'

    3. The attempt at a solution
    I wrote down:

    m * g * (d/4) = M * g * d

    (m/4) = M

    m = 4M

    Thus, the ratio is 4M : 1 m, which gives answer 1.

    However, the solutions say that the answer is 5.

    Could anyone please weigh in, and thanks in advance for the help!
  2. jcsd
  3. May 7, 2016 #2


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    Science Advisor

    I agree with your answer.
  4. May 7, 2016 #3


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    Homework Helper
    Gold Member

    No, you have shown 4M=1m. Think of M and m as numbers there. What is M/m?
  5. May 8, 2016 #4
    ahh 1/4. Right, thanks!
  6. May 8, 2016 #5
    I have another method,
    For the system to be in equilibrium the centre of mass should lie exactly on the pivot.

    Assume the pivot to be at (0,0)
    assume M to be at (d,0)
    assume m to be at (-d/4 ,0)
    Applying the formula of center of mass
    x c.o.m. = (m(-d/4) +Md)/(m+M) = 0

    Md = md/4
  7. May 8, 2016 #6
    That sir is an awesome and time-saving method! Thanks a lot!!! Everyone thanks!!
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