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: Car on Icy Hill

  1. Jan 28, 2007 #1
    1. The problem statement, all variables and given/known data
    On an icy day, you worry about parking your car in your driveway, which has an incline of 13°. Your neighbor Ralph’s
    driveway has an incline of 8°, and Bonnie’s driveway across the street has one of 5°. The coefficient of static friction
    between tire rubber and ice is 0.15. Which driveway(s) will be safe to park in?

    2. Relevant equations
    Force of friction=F*u

    3. The attempt at a solution
    How can we know 'F' without knowning the mass of car?
     
  2. jcsd
  3. Jan 28, 2007 #2

    cristo

    User Avatar
    Staff Emeritus
    Science Advisor

    Just let mass=m, and leave it in the equations. When comparing the components of the forces in the horizontal direction, the masses will cancel.
     
  4. Jan 28, 2007 #3
    Here is what I just did...

    Sum of Forces in horz direction,
    F_f*cos@-F_n*cos(90-@)=0
    Since F_f=u*F_n
    0=0.15*F_n*cos@-F_n*cos(90-@)
    Divide by F_n, solve for @ to be 8.6 degrees. So both Ralph's and Bonnie's driveways will be ok?
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook