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Homework Help: Bicyclist riding down hill

  1. Nov 3, 2008 #1
    1. The problem statement, all variables and given/known data
    A bicyclist of mass 65kg (including the bicycle) can coast down a 6 degree hill at steady speed of 6km/h because of air resistance. How much force must be applied to climb the hill at the same speed and same air resistance?

    3. The attempt at a solution

    since it is at constant speed. the net force is zero.

    therefore the

    Fg (force due to mg) - Fr (air resistance force) = 0

    (mg sin 6) - Fr = 0

    Fr= mg sin 6 = 66.58N.

    For it to climb back the hill at the same speed and same air restance?

    the bicyclist have to tackle the two same force now = 66.58 + mg sin 6 = 133N.

    The model answer given is 130N.....but i got 133N...

    any mistake i have made?
  2. jcsd
  3. Nov 4, 2008 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    You haven't made any mistakes, perhaps the model answer has rounded to 2sf?
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