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Homework question, please help

  1. Apr 13, 2013 #1
    homework question, please help!! :)

    1. The problem statement, all variables and given/known data
    A 1500 kg car is parked on a 4 degree incline. The acceleration of gravity is 9.8 meters per second squared. Find the force of friction keeping the car from sliding down the incline. Answer in units of Newtons.

    2. Relevant equations
    What formula(s) would you use?

    3. The attempt at a solution
  2. jcsd
  3. Apr 13, 2013 #2


    Staff: Mentor

    one draw a force diagram and then use trig to break up the force of gravity into two components:
    - parallel to the incline
    - perpendicular to the incline

    Your frictional force needs to counteract one of those components. which one?
  4. Apr 13, 2013 #3


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    welcome to pf!

    hi julestux! welcome to pf! :wink:

    first, find the normal force …

    show us what you get :smile:
  5. Apr 13, 2013 #4
    the normal force I got was 14664.19
  6. Apr 13, 2013 #5


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    That's good. But I think you actually want the tangential force. That's what friction has to offset. And do specify units on a force.
  7. Apr 13, 2013 #6


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    (i haven't checked your result)

    ok, now take components (of all the forces) along the slope …

    they have to add to zero :wink:
  8. Apr 13, 2013 #7
    how do they add up to zero?:cry:
  9. Apr 13, 2013 #8


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    What do you mean by "how?" Add them up and set the sum equal to zero. It's a necessary condition if the object is stationary, and therefore unaccelerating.
  10. Apr 13, 2013 #9


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    yes :smile:

    julestux, are you confused by assuming static friction = µN ?

    it isn't, it's ≤ µN, you find out how much it is by summing the components to zero :wink:

    anyway, show us what you get for the compontents along the slope :smile:
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