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Positive or Negative Work?

  1. Sep 26, 2010 #1
    1. The problem statement, all variables and given/known data
    A car is rolling to the right and you try to slow it down by pushing on it to the left. You are doing

    A) positive work
    B) negative work
    C) no work until the car comes to a stop
    D) You can’t tell because I didn’t tell you which way was positive.

    2. Relevant equations
    Work = constant force * distance

    3. The attempt at a solution
    I think its might be A because you are transferring energy to the car thus positive work but I'm not quite sure. I was tempted to pick D, but after doing a little simulation in my head I chose otherwise.

  2. jcsd
  3. Sep 26, 2010 #2


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    Oh, you're 0 for 2....one more strike and you're out. Your equation for work is wrong...it's work = force times displacemnt times the cos of the angle between the 2. Which way does the force act on the car...and what is the direction of the displacement of that force?
  4. Sep 26, 2010 #3
    Well if I said the left was negative, and the right was positive then I'd be applying force in the negative direction while the displacement would be positive. Oh so it would be B then correct? Didn't think about working it out like that
  5. Sep 26, 2010 #4


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    Yes, correct. When the force and displacement are opposite, work is negative; when they are in the same direction, work is positive.
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