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Homework Help: Calculating Displacement with Friction and Air Resistance

  1. Dec 12, 2012 #1
    1. The problem statement, all variables and given/known data

    A car is rolling down a hill, it has a velocity of 54.22m/sec at the bottom of the hill. When it reaches the bottom of the hill, a fan begins to blow on it causing a drag force of 250N. Also, the tires create a friction coefficient of .1. The car eventually stops due to the Drag Force/Friction. Calculate how far the car will travel before stopping.

    I can't figure out how to take into account the drag force. I know that before taking drag force into account, the car can travel 27.66m. I'm not sure if that helps or not. All I need to know is what formula to use and where I implement the drag force! Also, my homework is due TOMORROW AT 3PM EST. Any help before then will be awesome.
  2. jcsd
  3. Dec 13, 2012 #2
    How did you come to the 27.66 m? show your calcs without the drag force and I'll help with implementing the drag force...
  4. Dec 13, 2012 #3
    First, I calculated for the Kinetic Energy which would be 1/2mv^2. 1/2(1700kg)(54.22m/sec) = 46,087J. Next, I calculated the impact friction would have: f=u(coeficcient of friction)F .1(1700)(9.8) = 1,666N. Then I calculted the work that would be done: Work = F(displacement) 46087J = 1,666N(displacement) then I divided 46087 by 1666 and came with 27.66M. If this is incorrect, could you tell me how to do it please? Thanks!
  5. Dec 13, 2012 #4
    I think if I tell you that you would realise how easy it is. So you have an object working to the right with kinetic energy = 0.5*mv^2 your answer here is incorrect, do the calculation again... Now what is the total forces working against the vehicle? friction and drag, draw a FBD for your vehicle... Your methodology is good and accurate just combine everything now... The total force on the car is not just friction?
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