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

  1. Oct 31, 2005 #1
    A person pulls her 70 N bag 200 meters at a constant speed.
    The force exerted is 40 N at 50 degrees.

    I can figure out the work the person does (5142 J).

    But I'm having trouble figuring out the 'work done by the force of friction'

    I know that Wfriction = delta KE + delta PE
    ...Since the speed is constant KE should be 0, but I'm not sure what to do about PE.. I know PE = mgy and delta PE = PEfinal - PEinitial but since it's a horizontal surface wouldn't that be 0? I must be doing something wrong because it can't be 0..
     
  2. jcsd
  3. Oct 31, 2005 #2
    The net force is ____ because the bag's velocity and speed are _____ which means the force by the ______ equals the force of _______.
     
  4. Oct 31, 2005 #3
    Just to make sure I understand

    The net force is _0___ because the bag's velocity and speed are __constant___ which means the force by the _parallel component of force(40N*cos(50))_____ equals the force of _friction______?
     
  5. Oct 31, 2005 #4
    You've got it.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook