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Kinetic Friction and Incline for a Car

  1. Apr 12, 2016 #1
    1. The problem statement, all variables and given/known data
    jkMNHCG.png

    2. Relevant equations
    friction:
    f = μN
    incline angle: θ = arctan(1/10)
    summation of forces in y: N - mgcosθ = 0
    summation of forces in x: -f - mgsinθ = ma (?????)

    3. The attempt at a solution
    For this problem, I set the x-axis going up the incline and the y-axis normal to said x-axis. When I drew the FBD, the part that did not make sense to me was the summation of forces in the x-axis. The question wants the car to accelerate UP the incline, but the two forces I draw for the FBD both point down the incline. One of the forces is the x-component of the weight, mgsinθ, and the other is the friction. I know the weight's x-component direction is right, so the wildcard is the friction. Isn't friction opposite to the direction of motion?
     
  2. jcsd
  3. Apr 12, 2016 #2
    I just had a thought... is friction the force which drives the car forward? The wheels spin in the negative x-direction (with respect to the ground) so the friction points to the positive x-direction. If that were the case it would make a lot of sense!
     
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