Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Nonconservative forces

  1. Jun 30, 2004 #1

    I've been needing help with a question in my textbook. It seems so stupidly easy, but I can't get it. (Ironically enough, I understood all the others).. here's the question:

    A bicyclist rides 5.0km due east, while the resistive foce from the air has a magnitude of 3.0N and points due west. The rider then turns around and rides 5.0km due west, back to her starting point. The resistive force from the air on the return trip has a magnitude of 3.0 N and points due east. Find the work done by the resisitve force during the round trip.

    Here's what I did:
    W = Fd
    W = (3.0N)(5.0km) = -15J
    since its a round trip, I doubled it and get -30J, but the book says that the answer is -30000J

    Any help would be greatly appreciated!
  2. jcsd
  3. Jun 30, 2004 #2


    User Avatar
    Science Advisor

    You have a "units" problem. A "Joule" is defined as the work done by a force of 1 Newton acting over a distance of 1 meter- not 1 kilometer.

    How much work is done by a force of 3 N acting over a (total) distance of 1000 m?
  4. Jun 30, 2004 #3
    oh.. a UNITS problem.. I feel very stupid.. sorry for bothering you with that, but thanks! :)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook