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Mechanics, Uniform Circular Motion

  1. Dec 1, 2009 #1
    1. The problem statement, all variables and given/known data
    A flat racetrack viewed from above has curves with radius of 50.0 meters and 100. meters. A car having a mass of 1.00 x 10^3 kilograms moves counterclockwise around the track at a constant speed of 20.0 meters per second. It takes the car 20.0 seconds to travel from C to D.

    Radius = 50.0 meters and 100. meters
    Mass = 1.00 x 10^3 kilograms
    Speed = 20.0 m/s
    Time = 20.0 s from C to D

    1. What is the magnitude of the net force acting on the car while it is moving from A to B?
    2. Calculate the net force acting on the car while it is moving from B to C.
    3. Calculate the distance from C to D.
    4. Compare the magnitude of the centripetal acceleration of the car while moving from D to A, to the magnitude of the centripetal acceleration of the car while moving from B to C.
    5. Compare the magnitude of the car's momentum at D to the magnitude of the car's momentum at B.
    6. Compare the magnitude of the centripetal acceleration of the car at A to the magnitude of the car's centripetal acceleration at A if additional passengers were riding in the car.

    2. Relevant equations

    2 = {Pie}r / t
    ac = v^2 / r
    Fc = ma{c}

    3. The attempt at a solution
    I'm sorry I just don't understand but I know the equations to use. Ok, but ill attempt to do it at least.
    1. I don't know anything much about net force.
    Would this be the equation? a = Fnet / m
    I'm just really sorry but I only know about centripetal force, average speed and the centripetal acceleration. I dont know about the magnitude of the net force only magnitude of centripetal acceleration.

    I would really appreciate it if you can help me. I do understand I should learn this but I wish I knew the equation to use for net force.

    Okay I understand 91.
    91. ac = v^2 / r
    ac = (20)^2 / 50
    ac = 8 for D to A

    ac = (20)^2 / 100
    ac = 4 for B to C

    Is this correct? Thanks I really appreciate this.
     
    Last edited: Dec 1, 2009
  2. jcsd
  3. Dec 1, 2009 #2

    Delphi51

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    Homework Helper

    Welcome to PF, Priscilla!
    It is difficult to understand the question without seeing the diagram. Perhaps you could sketch it in a paint program, save the painting to a photo site like photobucket.com and post a link here.

    Yes, Fnet or Ftotal is always equal to ma.
    Likely the only force you have on those turns is Fc = mv²/r = ma so your calc is probably correct.
     
  4. Dec 2, 2009 #3
    Okay, here is a diagram for the problem. Thanks a lor!
     

    Attached Files:

  5. Dec 2, 2009 #4

    Delphi51

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    Homework Helper

    Great, the diagram really helps. Your work so far looks very good.
    I see some of the questions involve no calculations, like #1.
     
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