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Combining two equations

  1. Oct 17, 2004 #1


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    I have the following problem that I can't seem to solve.

    Combine these two equations:
    TR = I(alpha) *Newton's 2nd law of Rotation for the wheel
    T - mg = ma *Newton's Second law for the mass
    to make this one:
    mg = I/R^2*a

    Note that a is much smaller than g

    I break it to:

    mg = I(alpha)/r - ma or I(alpha)/r ... unless (alpha) = a/r in which case ... hmmm

    First of all I notice that alpha and T are eliminated. Two variables gone for two equations?? (a is smaller than g, does that mean alpha is...?)

    Also, where does R^2 come from?

    I think T if force (F), R is radius (r)
    I is moment of inertia, alpha is angular accel, m is mass, g is (duh) gravitational constant and a should be acceleration
  2. jcsd
  3. Oct 17, 2004 #2
    I couldn't remember what "I" is defined as in terms of algebraic expression.

    But "R^2" comes from acentripedal = v^2/r = alpha; after you combine

    mg = ma - Ialpha/r, you plug in v^2/r for alpha, you get /r^2
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