Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Calculating error

  1. Feb 2, 2010 #1
    1. The problem statement, all variables and given/known data

    The expression for the slope of the graph of [tex](m_{1} - m_{2})[/tex] versus a is given by [tex]m = (m_{1} + m_{2} + m_{p})/g[/tex]. What is the expression for the error in the mass of the pulley, [tex]m_{P}[/tex]?

    3. The attempt at a solution

    My answer is [tex]\delta_{p} = g\delta_{m} + \delta_{m1} + \delta_{m2}[/tex]

    I don't think this is right. Can someone show me where I went wrong?
    Last edited: Feb 2, 2010
  2. jcsd
  3. Feb 2, 2010 #2


    Staff: Mentor

    None of this makes any sense, as far as I can tell. In your first sentence you say
    If you are graphing m1 - m2 vs. a, why doesn't a appear in the equation?
  4. Feb 2, 2010 #3
    I'm not sure if this would help, but [tex](m_{1}-m_{2})g = (m_{1}+m_{2})a[/tex]

    I think g might have been substituted for a.
  5. Feb 2, 2010 #4


    Staff: Mentor

    Here's where I think this is going. You have m = (1/g)(m1 + m2 + mp), so
    [tex]dm = \frac{\partial d m}{\partial m_1}\Delta m_1 + \frac{\partial d m}{\partial m_1}\Delta m_1 +\frac{\partial d m}{\partial m_1}\Delta m_1[/tex]
    [tex]= (1/g)[1 \Delta m_1 + 1 \Delta m_2 + \Delta m_p] [/tex]

    Now solve for [itex]\Delta m_p[/itex] in terms of the other quantities.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook