1. Not finding help here? Sign up for a free 30min 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!

Calculate the work done by friction

  1. Oct 31, 2011 #1
    1. The problem statement, all variables and given/known data
    You have a level track. You push a cart with mass = 1.12[kg].
    You measure the initial velocity to be 0.57[m s-1].
    2 seconds later, you measure the velocity to be 0.427[m s-1].


    2. Relevant equations
    What is the work (reported in mJ) that friction did on the cart?


    3. The attempt at a solution

    W(f)=F(f) x d
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Oct 31, 2011 #2

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Welcome to PH.

    You need to show us your work so we can help you.

    Hint: What does the Work-Energy Theorem say?
     
  4. Nov 1, 2011 #3
    W= deltaK = 1/2m(Vf^2 - Vi^2)

    W=1/2 (1.12kg) [((0.427m/s)^2) - ((0.57m/s)^2)]

    W= -0.0798 kg m/s

    Is this the work done by friction though? or the cart?
     
  5. Nov 1, 2011 #4

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    On what object would the cart do work?

    Friction slows the cart, so it does negative work on the cart, so your answer seems reasonable.
     
  6. Nov 1, 2011 #5
    Okay that makes sense. thank you.

    So if i were to calculate work done by friction, but this time I'm given distance and delta K, would I use Wncf=fd where f=(deltaK)/d or work energy theorem?
     
  7. Nov 1, 2011 #6

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    That gives you the friction (force) itself.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook