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!

Work done against friction for a car with 125 KJ KE.

  1. Nov 5, 2013 #1
    "A 1200kg car as kinetic energy 125kJ at the bottom of a 20 degree slope. It rises to a height of 10m. Calculate work done against friction."

    Relevant equations:

    Work = force x distance in direction of that force

    Work = KE = 1/2 x m x v^2

    I'm not really sure where to start...tried several things but haven't got anywhere.

    For example:

    Work done = KE
    125000J = 1/2 x 1200 x v^2
    V^2 = 125000/600 = 208.3
    V = 14.4 m/s

    Or

    GPE at top of slope = mgh
    1200 x 9.81 x 10 = 117,720

    Energy lost = 125000 - 117720 = 7280 J

    But neither of these answer the question.

    Also tried

    Distance travelled = 10/sin20 = 29.24m

    So f = 125000/29.24 = 4274.9J buy apparently that's wrong.

    Someone please help? :-)
     
  2. jcsd
  3. Nov 5, 2013 #2

    Doc Al

    User Avatar

    Staff: Mentor

    This is the one you want.

    If that's not right: Are you sure it says "rises to a height " of 10m? Maybe they meant that it travels up the ramp a distance of 10 m?
     
  4. Nov 5, 2013 #3
    I tried it that way as well and none of the answers match up (it's multiple choice). Hm, perhaps I copied the answers/some of the question down wrong!
     
  5. Nov 5, 2013 #4
    So just to confirm, would the energy lost be the same as the work done against friction?
     
  6. Nov 5, 2013 #5

    Doc Al

    User Avatar

    Staff: Mentor

    Yes, assuming friction is the only source of energy "loss".
     
  7. Nov 5, 2013 #6
    What are the choices?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Work done against friction for a car with 125 KJ KE.
Loading...