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Forces - Newton's Laws Problem

  1. Oct 11, 2013 #1
    1. The problem statement, all variables and given/known data

    A 1200 kg car travels at 50 km/h and experiences air resistance of 5000 N and road friction of 2200 N. If the wheels push with a force of 7500 N, what is the car's acceleration?

    2. Relevant equations

    a = ƩF/m

    3. The attempt at a solution

    I got ƩF = 8590 N [E52°S] then plugged it into the equation,
    but it did not work to the correct answer of 0.250m/s^2.

    I'm thinking I probably had to make use of the 50 km/h variable somewhere, which I didn't.
    When and where would that apply...?
     
  2. jcsd
  3. Oct 11, 2013 #2

    Doc Al

    User Avatar

    Staff: Mentor

    How did you find that sum? Realize that the forces point in different directions. Where did that angle come from?
     
  4. Oct 11, 2013 #3
    how did you get ƩF=8590 [E52°S]?

    To me it seems you interpreted it wrong. Its a one dimensional problem, but by the looks of your answer it is a vector result.

    car is being pushed forward by 7500 N...........backwards by air resistance of 5000 N........again backwards by road friction of 2200 N.

    ƩF=ma

    try again you should arrive at the right answer.

    P.S. - No offense, but please consider revising the key points of the chapter associated with Forces.

    Edit : Doc Al got there first!!!
     
  5. Oct 11, 2013 #4
    ohh, okay i don't know why i thought air friction was in the direction north.
    but thank you and yes, i just started this unit yesterday, i will make sure to revise!
     
  6. Oct 11, 2013 #5
    great, glad you appreciate the help!!!:smile:
     
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