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Homework Help: Finding mass of this car

  1. Nov 13, 2012 #1
    1. The problem statement, all variables and given/known data

    Each of the four wheels of a car pushes on the road with a force of 4.0 x 103 N [down]. The driving force on the car is 8.0 x 103 N [west]. The frictional resistance on the car is 6.0 x 103 N [east]. Calculate the mass of the car.

    2. Relevant equations

    F = ma
    Fnet = F1 + F2

    3. The attempt at a solution

    Fnet = F1 + F2
    Fnet = FA - Ff
    = 8.0 x 103 - 6.0 x 103
    = 2000 N [west] ​

    Total force of all four wheels:
    (4.0 x 103 N [down]) x 4
    = 16000 N [down]​

    FN = 16000 N[up]
    But this is only part of the Normal Force, because the rest is coming from the weight of the car.

    It seems to me that there isn't enough info to find mass?
  2. jcsd
  3. Nov 13, 2012 #2
    Wait, is the normal force simply the force of all the wheels ?
  4. Nov 13, 2012 #3


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    Staff: Mentor

    That would be my answer. The horizontal movement forces in this case would not seem to affect the vertical weight.
  5. Nov 13, 2012 #4


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    Staff: Mentor

    Actually, it looks from the sum of the horizontal forces that the car is accelerating, which will unbalance the weight on the front and back tires, but the sum of all 4 should be the same as at rest, I would think.

    Hmm, need to think more about that...
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