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Homework Help: Perpendicular force required to stop an object, with respect to friction

  1. Oct 13, 2011 #1
    1. The problem statement, all variables and given/known data
    What force have to be applied to stop an polymer object with mass 5 gram and velocity 0.1 mm/s to stop in 0.2 mm? The polymer object touches a human skin at one side only, whereby friction Ff has a influence in the stopping process.

    The object is moving to the left. In contrast to a normal problem, the stopping force is not a opposite one, but a perpendicular force. See image below.

    _________________________________________ (human skin)
    ← □ (object moves with directon to the left)
    ↑ (perpendicular force - to the object and the human skin - to stop the object)

    2. Relevant equations
    F = ma

    3. The attempt at a solution
    To my knowledge, the formula F = ma is used to calculate the value of a opposite force to stop a object. Which formula do you use in case of a perpendicular force with respect to friction?

    Many thanks!
  2. jcsd
  3. Oct 14, 2011 #2


    User Avatar

    Staff: Mentor

    If friction is causing the stopping force (in the direction opposing the motion), then you use the equation for frictional force:

    F = μ N

    Where μ is the coefficient of friction, and N is the Normal force (the force pushing the object onto the skin in this case)...
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