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Homework Help: Synthesis Problem

  1. Mar 12, 2015 #1
    A solid balsa cube of side length L = 16.0” and mass M = 8.60 kg is at rest on a horizontal table top. It is constrained to rotate about a fixed and frictionless axis, AB, along one edge of the cube. A bullet of mass m = 50.0 g is fired with speed v at the other side of the cube, at height a = 12.0” above the table surface. The bullet becomes embedded in the cube in the middle of the face opposite face ABCD. Find the minimum value of the speed v required to tip the cube over, so that it falls on face ABCD. You may assume that the bullet mass m is small enough, compared to M, that it does not change the rotational inertia or center of mass of the cube after it embeds.

    I've been working on this problem for a while and the only answer i got was 921 m/s but i dont think thats right... if someone could help me set up the problem that would be appreciated.
  2. jcsd
  3. Mar 12, 2015 #2
    How did you get to 921 m/s? Then we can see where you went wrong.
  4. Mar 12, 2015 #3
    I honestly have no idea how to set it up, i just plugged it in to an equation my professor showed me on a similar problem today. which is mvr=.5ml^2 +md^2
    so .05*v*4=1/12 *8.6 *16^2 +.25*4^2
  5. Mar 13, 2015 #4


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    That sounds like a recipe for failure. There is too much specific detail here for such an approach. There's no substitute for understanding and applying the general principles.
    I gather that AB is an edge on the table. Have you drawn a diagram? What general principles have you learnt that can be applied?
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