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!

Please help with possible test question

  1. Feb 13, 2006 #1
    Johnny jumps off a swing, lands sitting down on a grassy 20 degree slope, and slides 3.5 m down the slope before stopping. The coefficient of kinetic friction between grass and the seat of Johnny's pants is 0.5.What was his initial speed on the grass?

    now i know the answer is 2.96m/s, but i dont know how to get at it...

    heres what i tried:

    Fn= mgsin20


    mgsin20-Ff= ma

    mgsin20- .5mgcos20 = ma

    (m's cancel out)
    a=2.88 m/s^2

    Vi^2= 0 + 2(-2.88)(3.5)
    Vi= 4.49 m/s

    but this is definately wrong..... how do i get the real answer?
    Last edited: Feb 13, 2006
  2. jcsd
  3. Feb 13, 2006 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Your method is perfect, but redo the calculation for "a".
  4. Feb 13, 2006 #3
    thank you, my friend :biggrin:
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Please help with possible test question
  1. Please help on test (Replies: 5)