1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Work-energy theorem please help, not sure what I am doing wrong.

  1. Feb 15, 2010 #1
    On an essentially frictionless, horizontal ice rink, a skater moving at 6.0 m/s encounters a rough patch that reduces her speed by 42 \% due to a friction force that is 20 \% of her weight.

    Use the work-energy theorem to find the length of this rough patch.

    i do: [.42 * (.5) * (6)^2]/ [.2 * 9.8]=3.85
    but i get the wrong answer can anyone help, does the answer need to be negative, what am i doing wrong.
  2. jcsd
  3. Feb 15, 2010 #2


    User Avatar
    Homework Helper

    What does the work-energy theorem state?

    What is the change of the KE if the speed is reduced to 42% of the original 6 m/s ?

  4. Feb 16, 2010 #3
    K_2-K_1 where k=1/2*m*v^2, thank you, it would be .58v not .42, in the equation
    -.2gs = (1/2)mvf^2 - (1/2)mvi^2 where the m cancel
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook