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Homework Help: Centripital forces Question

  1. Apr 18, 2009 #1
    1. The problem statement, all variables and given/known data
    1. a) Determine the speed required by a coaster that would cause a rider to experience a normal force of 2mg at the top of a clothoid loop where the radius is 12meters.

    2. Relevant equations

    3. The attempt at a solution

    http://i160.photobucket.com/albums/t161/mike_302/physicsq.jpg [Broken]

    That is my attempt at aa solution. Now, the only problem is that I get a square root negative... Obviously imaginary. Can't do it. But if I made the number positive, I get the right value of 19m/s for speed.

    Somewhere/somehow, I need to cancel out the negative in there. Can someone explain how?

    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Apr 18, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Hint: In which direction is the coaster's acceleration? Is that positive or negative?
  4. Apr 18, 2009 #3
    oh! okay. so acceleration is down. GOT IT! WOW! HUGE thanks!
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