5 thoughts on “3.39”

    1. Yes, unless the problem statement defines positive directions of motion we must choose a direction, and we are free to choose it however we like. In my videos I will always choose consistent directions (i.e. all masses are able to move in their positive directions simultaneously, and thus all my kinematic constraints come out with positive coefficients.

      If you choose a different coordinate your EOM may look different, but it will be equivalent if you have performed the analysis correctly.

  1. When deriving the equilibrium EOM, (12:15), I do not see how -m_1g\sin(\alpha) on the left hand side cancels out the -2m_1g\sin(\alpha) on the right hand side. Am I missing something?

    1. Good catch! I made an error, if you look at the work in red you'll see that I forgot to write a 2 on the second line. Where I wrote

      x_0 = \frac{(m_2 - m_1 \sin(\alpha))g}{2k}

      it should have been

      x_0 = \frac{(m_2 - 2m_1 \sin(\alpha))g}{2k}

Leave a Reply

Tutoring for Statics, Dynamics, and Controls courses at Texas A&M