Homework H.4.I

NOTE: All surfaces are smooth. Unfortunately, this information was omitted from the problem statement.



STEP 1 - FBD: Draw a SINGLE free body diagram (FBD) of the system including Block A, Block B and the rigid bar. From this, determine which forces do non-conservative work on this system, if any.
STEP 2 - Kinetics:  Write down the work/energy equation.
STEP 3 - Kinematics: Consider the location of the instant center for bar AB. This will be the key to the kinematics that you need to solve this problem.
STEP 4 - Solve



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7 thoughts on “Homework H.4.I”

  1. How does B influence this problem mathematically and conceptually? My current work energy equation has no B influence, and I'm not sure how kinematics or the instant center helps, as the only non time dependent kinematics equation gives the same exact result as my work energy equation. Also how do I deal with differing directions in force/velocity etc for the work energy equation?
    Basically I'm lost during/after creating the work energy equation

    1. I am not sure of your questions here.

      Let me try to point out what I think are the important aspects of the problem. First, the kinetic energy for the system is the sum of the kinetic energies of A and B. Secondly, the potential energy for the system is the sum of the potential energies of A and B. The kinematics part of the problem (Step 3) allows you to relate the motion of A and B, something that is required in order to solve. In general, the relationship between the speeds of A and B is a little complicated; however, for the particle Position 2, it greatly simplifies.

      I hope that some of this helps.

      1. Yeah that helps, I had it explained to me as well, It took me a second to wrap my head around putting in B and A values and just ignoring direction

        1. Although I am now confused at how to find angular velocity for the rigid body kinematics equation for the system without relating it to the Va and Vb, which leads to a ridiculously complex system with tons of trig for the kinematics part, which doesn't seem right.

          1. You don't need to find angular velocity. Use the fact that L is the hypotenuse of a triangle with the other sides being sa and sb (vertical and horizontal distances from the corner) to get an expression for L in terms of sa and sb. Differentiate this expression to get an expression with both va and vb, so that you can get vb in terms of va.

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