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!

Homework Help: Kinematic/Dynamic question

  1. Sep 24, 2012 #1
    1. The problem statement, all variables and given/known data
    A sled takes off from the top of a hill inclined at 6 degrees to the horizontal. The sled's initial speed is 12 m/s. The coefficient of friction between the sled and the snow is 0.14. Determine how far the sled will slide before coming to rest.

    2. Relevant equations
    vFsquared=vIsquared + 2a(d)
    vf= velocity final vI= initial velocity a=accel. d=displacement.

    3. The attempt at a solution
    Well I didn't get very far because I don't have enough variables, I need mass! I obviously need to find accelerating, what would my f=ma statement be? I thought it would be Fapp - Ffriction = ma........help?
  2. jcsd
  3. Sep 24, 2012 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Perhaps worth remembering the definition of coefficient of friction. It's the ratio of two forces one of which depends on the mass. This means that mass sometimes cancels in some problems so it's not allways needed.

    Draw the free body diagram and write equations for the forces.
  4. Sep 24, 2012 #3
    Fg - Ff = ma
    mgsin(theta) - umgcos(theta) = ma
    I have two masses to remove, not just one :/ So i can't just simply simplify to:
    gsin(theta) - ugcos(theta) = a right?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook