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Finding ratio of masses of two blocks

  1. May 8, 2016 #1
    1. The problem statement, all variables and given/known data
    1. Two crates are stacked on top of each other on a horizontal floor. The coefficient of static friction between Box A and Box B is 0.6. The coefficient of static friction between Box A and the floor is 0.2. A force of 100 N is applied parallel to the floor on Box B. The boxes move together along the floor. The ratio of the mass of Box A to Box B is possibly
    1. 1) 5:1
    2. 2) 5:2
    3. 3) 4:1
    4. 4) 3:1
    5. 5) 1:2

    2. Relevant equations

    none so far
    3. The attempt at a solution
    Hi people. I was trying to figure out how to solve this problem, but I do not even have any hints of an idea so far. Could anyone please help me gets started?
    Thanks in advance!
     
  2. jcsd
  3. May 8, 2016 #2

    CWatters

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    For the boxes to move friction between A and B must be greater than between A and the floor.

    Write equations for both and set up that inequality. Rearrange.
     
  4. May 9, 2016 #3
    Why is this so?
     
  5. May 9, 2016 #4

    CWatters

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    Think about how the applied force is transmitted to the lower box.

    Drawing a FBD for the lower box may help.
     
  6. May 9, 2016 #5

    CWatters

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    You posted one or two similar questions and they all depend on you understanding the forces acting on the lower box.
     
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