1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Tough Question?

  1. Dec 3, 2008 #1
    A bicylcist of mass 80 kg (including the bike) can coast down a 3.4 deg hill at a steady speed of 9.0 km/hr. Pumping hard, the cyclist can descend the hill at a speed of 30 km/hr. Using the same power, at what speed can the cyclist climb the same hill? Assume the force of air resitance is directly proportional to the speed v; that is Fsubfr=bv, where b is a constant.

    Not really sure how to approach this..
  2. jcsd
  3. Dec 3, 2008 #2


    User Avatar
    Science Advisor
    Homework Helper

    When he is coasting down the hill the component of gravity along the road balances the force of air resistance at 9km/hr. Figure out what that resistance force (F_fr) actually is since F_fr+F_g=0. When he's pumping hard at 30km/hr the resistance force is 30/9 times what it used to be. If the force he is exerting at 30km/hr is F_p then you now have F_p+F_g-(30/9)*F_fr. Figure out F_p. When he's going uphill F_g reverses. What's the new resistance force? Can you use that resistance force to figure the velocity?
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Tough Question?
  1. Tough question (Replies: 1)

  2. Tough moments question (Replies: 9)