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Homework Help: Kinetic Energy/Forces problem

  1. Oct 26, 2009 #1
    1. The problem statement, all variables and given/known data
    A car and driver weighing 5490 N passes a sign stating “Bridge Out 29.3 m Ahead.”
    She slams on the brakes, and the car decelerates at a constant rate of 10.9 m/s2.
    The acceleration of gravity is 9.8 m/s2 .
    What is the magnitude of the work done stopping the car if the car just stops in time to avoid diving into the water?
    Answer in units of J.

    2. Relevant equations
    KE = 1/2mv^2
    Ff = u * FN
    FN = mg
    F = ma

    3. The attempt at a solution
    a = -10.9
    Fg = 9.8

    need help in setting this problem up... i've never seen something weigh in N before is that important or relevant in any way? would I plug that into F = ma to find mass?
    help please!
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Oct 26, 2009 #2


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    Homework Helper

    If the weight is 5490 N, can you find the mass of the person+car ?

    If the deceleration is -10.9 m/s2 , can you get the force of friction acting on the car?

    If you have the frictional force, can you find the work done by this force given the distance?
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