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Homework Help: 2 boxes on flat ground and an incline

  1. Oct 14, 2009 #1
    1. A 10 kg box on a level surface is attached by a weightless, unstretchable rope to a 7.0 kg box which rest on a 30 degree incline. Find the rate of acceleration and the tension in the rope if... a) there is no friction ... b) coefficient of friction is 0.10 for both boxes

    2. F_net = m*a

    3. Honestly, I'm not sure where to start
  2. jcsd
  3. Oct 14, 2009 #2


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    Start with the box on the slope. Draw the force of gravity straight down and calculate its size in N. Draw a pair of vectors that begin and end in the same place as that first one, an arrow along the slope and another straight into the slope. Use trigonometry to figure out the size of each of these vectors. The force into the slope is cancelled out (the slope pushes back equally), so it is the component along the slope that causes the two masses to accelerate. Use F = ma.
  4. Oct 14, 2009 #3


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    Do you know how to draw free body diagram? Identify the various forces acting on each body.
    Find the net force acting in the downward direction. From that find the acceleration.

    Edit: Hi Delphi51, we are racing.
  5. Oct 14, 2009 #4
    So is the F_net = F_gravity parallel - F_tension - F_friction? because that is what I got after drawing a free body diagram...

    EDIT: and now I'm trying to solve and I'm getting an expression with two variables - tension and acceleration
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