Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

What is its speed after traveling 1.00 m on the rough surface?

  1. Dec 2, 2003 #1
    physics hw help ASAP thx!!!!

    thx so much, here they are:

    48. A block of mass 0.6 kg slides 6.0 m down a frictionless ramp inclined at 20 degrees to the horizontal. It then travels on a rough horizontal surface where coefficient of kinetic friction is 0.50.
    a) what is its speed after traveling 1.00 m on the rough surface?
    b) what distance does it travel on this horizontal furface before stopping?

    68. An electron moves with a speed of 0.995c.
    a) what is its kinetic energy?
    b) if you use the classical expression to calculate its kinetic energy, what percentage error would result?

    k = mc^2((1/(1-(v/c)^2))-1)

    thx a lot
  2. jcsd
  3. Dec 2, 2003 #2


    User Avatar
    Science Advisor

    Re: physics hw help ASAP thx!!!!

    Greetings !

    First of all welcome to PF ! And, as a member, you should
    know that there are certain guidelines in every forum
    here and the main guideline of this forum is that you
    have to show your attempt at a solution and not just
    ask for one.

    I'll give you some general hints though - in the first
    question you'd better use energy calcs. Find the energy
    at the bottom and think how you can compare it to the
    energy lost due to friction on the surface.

    In the second, well, just use the formula after you
    understand what its parts mean. :wink:

    Live long and prosper.
  4. Dec 2, 2003 #3
    oh ok

    well for the first one i found the frictional force that's retarding the energy of the object, so thats friction coefficient x normal force x distance, 0.5 x 0.6 x 9.8 x cos20 = 2.76, the distance is one.
    then i subtract the total work which is 0.6 x 9.8 x 6sin20 = 12.07 with 2.76 and get 9.31 J. ok, now wut happens? i spent about 3 hours on this problem already, please help!
  5. Dec 2, 2003 #4
    Correct, but that's happening on the horizontal part, not the ramp, right? Please redo.
    You should use the formula for kinetic energy.
    T = \frac{1}{2}mv^2.
  6. Dec 2, 2003 #5


    User Avatar
    Science Advisor

    The ramp is frictionless...
    You've spent 3 hours on it and still didn't realize the ramp is frictionless? Maybe your problem is English.
  7. Dec 2, 2003 #6
    naw man the problem says "on the rough surface"
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook