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: Friction and Work with an object sliding down a Ramp Problem!

  1. Sep 20, 2009 #1
    A 70 kg crate starting at rest slides down a rough ramp 4.0 meters long, inclined at 30 degrees above horizontal. At the bottom, it is moving at 5.0 m/s. what was the work done by friction on the crate???

    A. -500 Joules
    B. 500 Joules
    C. 460 Joules
    D. -460 Joules
    E. 0.0 Joules

    I got this answer wrong and i was wondering why... so here is my work. i got the height to be 2meters by using sin 30

    Mgh - Wf = 1/2MV^2

    70 * 9.81 * 2 - wf = .5 * 70 * 5.0^2
    875 - wf = 1373.4
    wf =1373.4-875
    wf = 500 joules

    so i got positive 500 joules. can any body tell me what the answer truly is and what i did wrong?? thank you alot!!
  2. jcsd
  3. Sep 20, 2009 #2


    User Avatar
    Science Advisor
    Homework Helper

    Last edited by a moderator: Apr 24, 2017
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook