1. Not finding help here? Sign up for a free 30min 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!

Coefficient of kinetic friction, need today

  1. Apr 30, 2010 #1
    coefficient of kinetic friction, URGENT need today

    The system shown in the figure below has an acceleration of magnitude 0.51 m/s2, where m1 =
    4.30 kg and m2 = 6.00 kg. Assume that the coefficient of kinetic
    friction between block and incline is the same for both inclines.

    Link to figure:
    http://img9.imageshack.us/img9/3437/figureyh.jpg [Broken]
    m1 is box on the left, m2 is box on the right. both angles are 35 degrees.


    a) find the coefficient of kinetic friction

    Here's what I tried:
    coefficient of kinetic friction = (gsinΘ - a) / gcos Θ
    and got .63668

    when i input my answer in the system said "your answer differs from the correct answer by orders of magnitude."

    b) find the tension in the string
    T= m1a + m1gsinΘ
    = 26.36 N

    system said "your answer differs by 10% of correct answer..."


    Please help. I need this by tonight. Thank you!!!
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Apr 30, 2010 #2

    hotvette

    User Avatar
    Homework Helper

    Re: coefficient of kinetic friction, URGENT need today

    Let's start with the basics. What equation of motion (i.e. [tex]\Sigma[/tex]F = ma) did you use for each mass?
     
  4. Apr 30, 2010 #3
    Re: coefficient of kinetic friction, URGENT need today

    ^

    (a)
    ∑ Fx = ma --> mgsinΘ - fk = ma
    ∑ Fy = 0 --> n - mgcosΘ = 0
    n = mgcosΘ
    and fk = mukn

    so muk = (gsinΘ -a) / gcos Θ
     
  5. Apr 30, 2010 #4

    hotvette

    User Avatar
    Homework Helper

    Re: coefficient of kinetic friction, URGENT need today

    I presume that's for m2. But, you forgot the force of the tension. Also, you need a similiar equation for m1. You'll then have two equations in two unknowns (T and mu) that can be solved by substitution.
     
    Last edited: May 1, 2010
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Coefficient of kinetic friction, need today
Loading...