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!

Internal Energy and kinetic friction

  1. Apr 11, 2009 #1
    1. The problem statement, all variables and given/known data

    Please help, Ive been struggling with this question for so long! We havent done internal energy so im not sure even where to really begin?

    A 10.0 kg block is dragged over a rough, horizontal surface by a 76.0 N force acting at 20.0° above the horizontal. The block is displaced 3.50 m, and the coefficient of kinetic friction is 0.300.

    What is increase in internal energy of the block-surface system due to friction?
     
  2. jcsd
  3. Apr 11, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    The change in internal energy equals the work done against friction.
     
  4. Apr 11, 2009 #3
    so if Ff= Uk.N...Then since Uk = 0.3 and N = 76.sin 20
    So Ff = 7.8, Hence W = 7.8 x 3.5 = 27.3? I tried that answer but it didnt work :S
     
  5. Apr 11, 2009 #4

    Doc Al

    User Avatar

    Staff: Mentor

    First you must correctly solve for the normal force. 76sin20 is the vertical component of the applied force, not the normal force.

    To find the normal force, analyze all the vertical forces that act on the block. Since the block doesn't accelerate vertically, vertical forces must sum to zero. Hint: There are three forces acting on the block that have vertical components; the normal force is one of them.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Internal Energy and kinetic friction
Loading...