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Homework Help: Average Total Force

  1. Oct 15, 2004 #1
    How do I go about solving this equation. Thanks.

    A 50kg cyclist, pedaling at 20 km/hr = 5.56m/s, climbs a 1 km hill in 30mins (.556m/s). What average total force on her bicycle is required for her to make it up the hill in this amount of time?

    I know that I have to find the acceleration to calculate the force, since N=(kg*m)/s^2. What equation would I use to accomplish this?
  2. jcsd
  3. Oct 15, 2004 #2


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    I think you left something out of the statement of the problem. Given the information you provided the cyclist could just as well be coasting on level ground without expending any energy.
  4. Oct 15, 2004 #3
    As the speed is uniform how could acceleration be there.
    Force required to make it up the hill is equal to the force to overcome friction, if mentioned, work done against the gravity.
    {i am not 100% sure but most probably it's true}
  5. Oct 15, 2004 #4
    Interesting...that is all the information I was given.

    So I wouldn't calculate acceleration since the cyclist is working against gravity.

    If I used f=mg (g=-9.8m/s^2)would that determine the total force?
  6. Oct 15, 2004 #5


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    Oh, the "1 km" hill must refer to the HEIGHT of the hill! If that's the case then you can do it! Basically, how much energy is required to raise the cyclist through 1 km?
  7. Oct 15, 2004 #6

    So I would use the pythagorean theorem to find the angle and then use equation a=g sin (theta). Once I have found "a" then I can calculate f=ma.

    Am I on the right track?

  8. Oct 15, 2004 #7

    Doc Al

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    This question is poorly formulated. Since the bike is not accelerating, the total force on it must be zero. But I'm guessing that they want you to figure out the frictional force parallel to the hill that the ground must exert on the bike tires to overcome gravity. Find the angle of the hill and the component of the weight down the hill. That's what the friction must overcome.

    You may want to ask your instructor for clarification.
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