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Roller Coaster Force Question

  1. Oct 13, 2018 #1
    1. The problem statement, all variables and given/known data:
    A child of mass 40.0 kg is in a roller coaster car that travels in a loop of radius 7.30 m. At point A the speed of the car is 15.0 m/s, and at point B, the speed is 15.6 m/s. Assume the child is not holding on and does not wear a seat belt.

    What is the force (in N) of the car seat on the child at point B? (Enter the magnitude.)

    0711e4f0e8708dce75c79380761364c9.png

    2. Relevant equations
    Fc = [(mv^2)/r]
    Fc = ma

    3. The attempt at a solution:

    I solved (a) and (c).
    I solved (a) by inserting the mass, speed, and radius into the equation [(mv^2)/r] and subtracting by (mass*gravity).
    My equation for (b) was [(mv^2)/r * cos30] - mg = [(40*(15.6^2)/7.3*cos30) - (40*9.8) = 762.8 N. That was incorrect. What's improper about my equation?
     
  2. jcsd
  3. Oct 13, 2018 #2

    SammyS

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    In what direction is the centripetal force at point B ?

    Also, is there any net force on the child at point B ?
     
  4. Oct 13, 2018 #3
    120 degrees(90+30)?
     
  5. Oct 13, 2018 #4
    I solved it by applying (cos 30) to mg instead of the centripetal force.
     
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