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: Frictional force and work problem

  1. Oct 15, 2009 #1
    1. The problem statement, all variables and given/known data

    A slide similar to der stuka is 35.0 meters high but is a straight slope,inclined at 45.0 degrees with respect to the horizontal. If a 60kg woman has the speed of 20.0m/s at the bottom and the work done by frictional force on the woman is -8.58 x 1000J, find the magnitude of the force of friction.

    2. Relevant equations

    Work done by frictional force = Frictional force cos 45 x horizontal distance

    3. The attempt at a solution

    using the equation:
    -8580 = F cos 45 x 35

    i am getting double the correct answer...can u tell me what am i doing wrong
  2. jcsd
  3. Oct 15, 2009 #2

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    You have to divide the height by cos 45

  4. Oct 15, 2009 #3


    User Avatar
    Science Advisor
    Homework Helper

    Hi billu77! :wink:
    yes … work done = force times distance, the height is 35, so the distance along the slide is … ? :smile:
  5. Oct 15, 2009 #4
    Your trig function is wrong. W=Fdcos(0), since the work the friction done is 8580 J, then W=8580. The distance the friction gone through is Hypotenuse, which is 35/sin(45) rather than 35*cos(45). F=8580/(35/sin(45))=8580*sin(45)/35=173. I am not sure what the initial velocity is doing though.
  6. Oct 15, 2009 #5
    thanks....i did not pay attention to the fact that frictional force is just acting along the slide and not at an angle.....appreciate ur help
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook