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I Help manipulating a Physics equation

  1. Nov 15, 2017 #1
    I'm reading my physics text book and the example has an equation of...

    mg-m(g/(1+M/2m)) = T

    manipulated so that it equals...

    T = mg/(1+2m/M)

    I'm not sure how to get this I tried to distribute the m to get...

    mg - mg/(1+M/2m)

    and multiplying mg by ((1+M/2m)/(1+M/2m)) but could not get the result the book got.
  2. jcsd
  3. Nov 15, 2017 #2


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    Staff: Mentor

    The approach is good so far. Make a single fraction out of it, then divide both numerator and denominator by M/(2m).
  4. Nov 15, 2017 #3
    It seems i missed some parentheses; it should be...

    mg - m(g/(1+(M/2m))) = T*

    T = mg/(1+(2m/M))*


    mg - mg/(1+(M/2m))


    Does that change the approach?
  5. Nov 15, 2017 #4
    I made into one single fraction of...

    (mg + (Mmg/2m) - mg)/(1+(M/2m))

    canceled out the mg's and multiplied the top by the reciprocal of the bottom...

    Mmg/2m x 1/(1+(M/2m)) = Mmg/(2m +2Mm/2m)

    Took out M from the denominator...


    Which is equal to...


    Did i do this correctly?
  6. Nov 15, 2017 #5


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    Only looked briefly - did not read it;
    Mere basic algebra. Nothing tough and nothing unusual.
  7. Nov 16, 2017 #6


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    Staff: Mentor

    Looks fine.
    Brackets around 2m denominatiors would have been more important than the other brackets by the way.
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