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Homework Help: Should Have Written it Down?

  1. Nov 5, 2009 #1
    [Very Urgent]Should Have Written it Down?

    1. The problem statement, all variables and given/known data
    Tomorrow I have to submit this analysis on a lab where you created a car that could carry an egg more then five meters across the floor while being powered by a fan. I created the car it pretty much didn't work since I had my wheels didn't turn that well, so I only made it as far as. I forgot to write down a instruction and now I am stuck on finding the frictional force.
    Results from the experiment

    Trials(With the egg):
    Trial 1: 2.9m in 90 secs
    Trial 2: 2.2 in 8.0 secs
    Trial 3: 2.6 in 7.0 secs

    Mass of the car 0.1426 kg (Without the Egg).

    A questions:
    When my teacher finished with the trials he then pulled out a spring scale attached it to the back of the car, turned the fan back on, and got a applied force of 0.6 N. The real question, calculate the magnitude of the frictional force exerts on the wheels. There is no coefficient, that is still to be found after this question is answered.

    2. Relevant equations
    Fn or Fg = m(g), Fa, Fk or Fnet = m(a)

    3. The attempt at a solution
    m = 0.1426 kg, g = 9.8 N/kg, Fa = 0.6 N

    Fn = (0.1426kg)(9.8N/kg)
    Fn = 1.39748 N

    Ff = Fg + Fa
    Ff = 1.39748 N + 0.6 N
    Ff = 1.99748 N?
    I am concerned about my answer since the applied force 0.6 N was found with the extra weight of the egg, and the mass was found without the egg. There is no coefficient.

    So if I can at least get something before noon Friday November 6, then I should be okay.
    Thank you.
    Last edited: Nov 5, 2009
  2. jcsd
  3. Nov 6, 2009 #2
    Re: [Very Urgent]Should Have Written it Down?

    If your teacher measured a force of 0.6N on the car at the point where it got stuck, than that would be the frictional force. Adding the normal force to that doesn't make sense.
    Finding a coefficient of friction will be hard, apparently you have wheel/axle friction, wheel floor rolling and/or sliding friction.
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