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Homework Help: Help with work and energy problem

  1. Feb 10, 2008 #1
    Hi i need help with this problem. The first part asks
    A car (m = 890.0 kg) travelling on a level road at 27.0 m/s (60.5 mph) can stop, locking its wheels, in a distance of 60.0 m (196.9 ft). Find the size of the horizontal force which the car applies on the road while stopping on the road. First solve this problem using work/energy concepts and then check your answer using kinematics/force law concepts.

    I solved this by finding the acceleration and plugging into formula F=ma=5402N

    The second part asks
    Find the stopping distance of that same car when it is traveling up a 18.9deg slope, and it locks its wheels while traveling at 27.0 m/s (60.5 mph). Assume that muk does not depend on the speed.

    I drew a free body diagram and came up with the following relationships
    F-fk-mgsin(18.9)=ma where F=5402N
    N-mgcos(18.9)=0

    How do I solve for the horizontal distance? Is it just the vertical component of the Force?
     
  2. jcsd
  3. Feb 10, 2008 #2
    I just tried using the formula Vf^2 = v0^2 + 2adx -- where final velocity=0, initial velocity is given, and i solved for a using the above equation F-ukmgcos(18.9)-mgsin(18.9)=ma. But I still didn't get the right answer..
     
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