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Homework Help: Another SUVAT and Newton's Second Law Question

  1. Nov 15, 2013 #1
    1. The problem statement, all variables and given/known data

    "The constant force resisting the motion of a car of mass 1500kg is 980N. If, when travelling at 48kmhr-1, the car is brought to rest in a distance 50m by applying the brakes, find the additional retarding force due to the brakes (assumed constant)

    2. Relevant equations

    SUVAT: v2=u2+2as, rearranged to a=(v2-u2)/2s

    Newton's Second Law: F=ma

    3. The attempt at a solution

    I used suvat (s=50m , u=48kmhr-1=13.3ms-1 [3.S.F.] , v=0ms-1 , a=a , t=t) to calculate the deceleration as 1.77ms-2 [3.S.F.], I then used F=ma, and found the force to be 2655N, is this right?
  2. jcsd
  3. Nov 15, 2013 #2
    2655N is the net retarding force.

    There are two retarding forces acting on the car.You need to deduct the constant force of 980N from the net force to get the force due to brakes .
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