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Force Applied to Box on Incline

  1. Dec 9, 2013 #1
    A force is applied to a box that is initially at rest on an inclined surface. The incline is at an angle θ=20.0° above horizontal. The mass is m=36kg and the vertical force is Fapp= 48N. Between the box and the inclined surface the coefficient of static friction, μs=.240 and a coefficient of kinetic friction, μk=.150. Use this information to fine the normal force in this situation.

    I am confused on where to start. Do I have to use both friction coefficients?
     
  2. jcsd
  3. Dec 9, 2013 #2

    haruspex

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    Is the applied force vertically up or vertically down? Either way, draw the free body diagram.
    Which coefficient to use depends on whether things move. You know it is initially at rest, so try supposing it stays that way. Use the information provided to find whether static friction is overcome. If it is, switch to using the coefficient for kinetic friction.
     
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