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: Potential Energy of a slide

  1. Feb 26, 2005 #1
    I've been doing this problem for the last 170 minutes. Literally, and I'm pissed.

    A 43-kg seal at an amusement park slides from rest down a ramp into the pool below. The top of the ramp is 1.75 m higher than the surface of the water and the ramp is inclined at an angle of θ = 35.0° above the horizontal. If the seal reaches the water with a speed of 4.40 m/s, what is (a) the work done by kinetic friction and (b) the coefficient of kinetic friction between the seal and the ramp?

    http://www.askthefool.com/Pic7.jpg [Broken]

    I've been doing W(non conservative) = 1/2 mv ^ 2 - mgh

    h = 1.75/sin(35)

    Don't know what's wrong.
    Last edited by a moderator: May 1, 2017
  2. jcsd
  3. Feb 26, 2005 #2
    I'd like help ASAP. I'm going to bed soon, so the sooner the better. I appreciate it.
  4. Feb 27, 2005 #3


    User Avatar
    Science Advisor

    {Initial Total Energy} = (1/2)*m*(v_i)^2 + m*g*h_i = 0 + (43)(9.8)(1.75) =
    = (737.45 J)
    {Final Total Energy} = (1/2)*m*(v_f)^2 + m*g*h_f = (1/2)*(43)*(4.40)^2 + 0 =
    = (416.24 J)
    {Delta Total Energy} = {Final Total Energy} - {Initial Total Energy} =
    = (416.24 J) - (737.45 J) =
    = (-321.21 J)
    = {Work Performed By Friction} = {-K*m*g*cos(35 deg)}*{1.75/sin(35 deg)} =
    = {-K*(43)*(9.8)*cos(35 deg)}*{1.75/sin(35 deg)} =
    = K*(-1053.188)

    A) {Work Performed By Friction} = (-321.21 J)
    B) {Coeff of Kinetic Friction} = (0.3050)

  5. Feb 27, 2005 #4
    This is homework that's submitted online. The due date is already passed, and I missed the problem but that dosen't matter. It's only one point.

    Howerver, we are still allowed to submit answer to check our work after the due date not for points, and i just tried the answers you provided and they are wrong. I've been getting those answers all night, trying a variety of ways.

    Any other ideas?
  6. Feb 27, 2005 #5
    I take that back. You/me are both right. The teacher emailed us saying that that problem was broken and that everyone got credit for it. Thanks for you're help.
  7. Feb 27, 2005 #6
    haha, I was about to say that your teacher is wrong when i read your first reply cause xanthym is correct lol :approve:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook