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What is the force of the track on the car?

  1. Nov 18, 2008 #1
    1. The problem statement, all variables and given/known data
    A roller-coaster has a mass of 500 kg when fully loaded with passengers. The car passes over a hill of radius 15 m. When at the top of the hill, the car has a speed of 8.0 m/s. WHat is the force of the track on the car at the top of the hill?


    2. Relevant equations
    F=ma


    3. The attempt at a solution
    I drew an FBD: wtih mg pointing down, N pointing up and static friction pointing to the left. ( I think this may be wrong, but I figured it may need static friction to stay on the track).
    Then when broken into i and j components I got:
    i= -MsN=-MV2/r ...(because the acceleration is centripical)
    then for j:
    I have N-mg=0
    N=mg
    and since it was asking for the force of the track on the car, I thought this was the normal force, so I just plugged in the values for m ang, and got 4.9 kN up. This is wrong, it is saying the correct answer is 2.8 kN up. Any suggestions on where I went wrong?
     
  2. jcsd
  3. Nov 18, 2008 #2

    PhanthomJay

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    The car is at the top of the hill; you seem to have your i and j mixed up. The centripetal accelertion is vertically down. Ignore friction.
     
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