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Acceleration and Momentum.

  1. Feb 17, 2016 #1
    1. The problem statement, all variables and given/known data
    A vehicle has a mass of 600 kg. Its engine provides a forward force of 1500 N, but the motion is resisted by a constant frictional force of 300 N.
    Calculate a) the acceleration of the vehicle,
    b) its momentum 6.0 s after starting to move.

    2. Relevant equations
    F=ma
    a=f/m
    Change in Moment = Force x Time.

    3. The attempt at a solution
    using a=f/m i can get acceleration easily.
    1500 - 300 = 1200
    1200 / 600 = 2.
    a = 2 m/s^2

    I think part B revolves around Change in Moment = Force x Time but I'm not sure as I can't see anyway to work it out using that formula but I'm unaware of another formula having time and monument in it.
    Time = 6.
    Force = 1200.
    6 x 1200 = 7200?
     
  2. jcsd
  3. Feb 17, 2016 #2

    ehild

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    Remember the definition of momentum p=mv, and how is the velocity related to acceleration and time.
     
  4. Feb 17, 2016 #3
    acceleration = change in V / t?
     
  5. Feb 17, 2016 #4

    ehild

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    yes, so what is the velocity after 6 s?
     
  6. Feb 17, 2016 #5
    a x t = change in V.
    2 x 6 = 12.
    p=m x v
    12 x 600 = 7200?
     
  7. Feb 17, 2016 #6

    ehild

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    Yes, but do no forget the unit. What is it?
    You see, it is the same result.
     
  8. Feb 17, 2016 #7
    7200 kg.m/s?
     
  9. Feb 17, 2016 #8

    ehild

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    Correct.
     
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