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Homework Help: At what angle will a box start to slide

  1. Apr 16, 2012 #1
    1. The problem statement, all variables and given/known data

    So there 2 boxes of nails being lifted at a construction site and one box is 20 kg and the other 10 kg. and the plank tilts towards the heavier box. if the coeficient of static friction is 0.4 draw a FBD for each box of nails and use it to calculate the angle at which each box begins to slide.

    2. Relevant equations

    3. The attempt at a solution

    |Fs| = µs|mg|

    20 Kg box is 78.4 N
    10 kg Box is 39.2 N

    And now im not sure how to continue...
  2. jcsd
  3. Apr 17, 2012 #2


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    Homework Helper

    When the board is at an angle, the normal reaction force will no longer equal mg in size, so you need to account for that.

    Question: is this situation really any different to having the boxes of nails on a ramp? It certainly would be if the crane lifting them was causing them to accelerate up or down, but if they are travelling at steady speed?
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