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Pushing a car & rolling resistance of tires

  1. Oct 12, 2012 #1
    I just want to know if I am understanding this correctly.

    I am wondering what effect the rolling resistance has on the motion of a car when pushed, or when rolling to a stop. The mass of the car is 1,000kg.

    I looked up on a table to find the rolling resistance coefficient of a normal car tire on asphalt and got .03 so that is the value I am using.

    Frr = .03 * 1,000kg * 9.8m/s² = 294 N

    a = 294 N / 1,000 kg = .294m/s²

    Question 1 :

    Does this mean that if a 1,000kg car is at rest in nuetral, and I want to get that car rolling, I would need to apply a force greater than 294 N before the car would even begin to roll?

    Question 2 :

    If this car was already in motion at say, 3m/s, would it come to a stop in about 10.2 seconds? (t = 3m/s / .294m/s² = 10.2s)

    I am ignoring any other sources of friction(ball bearings, etc), and the asphalt is perfectly level.

    Any help would be greatly appreciated. Thank you.
     
  2. jcsd
  3. Oct 12, 2012 #2
    That is a reasonable number for rolling resistance, which relates to the coefficient of dynamic friction. It would take more to get the car started.

    Think of a locomotive, which could never start a train of cars at the same time because the coefficient of static friction is too high. But because it only has to start one car at a time, it has no trouble keeping them moving.
     
    Last edited: Oct 12, 2012
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