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!

2 blocks, each on an inclined plane

  1. Jan 18, 2010 #1
    1. The problem statement, all variables and given/known data
    Two 2kg blocks are joined by a massless cord and pulley, ignoring friction, determine each block's acceleration using a free body diagram for each.

    Picture for visual aid: http://img27.imageshack.us/img27/2653/86460048.png [Broken]
    or a link: http://img27.imageshack.us/img27/2653/86460048.png [Broken]

    3. The attempt at a solution
    I did the free body diagrams and solved for the tension on the string to try to equate the two sides

    for the first block i got: T - mgsin30 = ma(1) so T = ma(1) + mgsin30
    for the second block i got: mgsin60 - T = ma(2) so T = mgsin60 - ma(2)

    The problem is the fact that i have two variables that i am solving for. I can't figure it out
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Jan 18, 2010 #2


    User Avatar
    Science Advisor
    Homework Helper

    Welcome to PF!

    Hi RonakPat! Welcome to PF! :smile:

    You're missing the obvious …

    the length of the string is constant, so a1 + a2 = 0. :wink:

    (some people call that a geometric constraint)
  4. Jan 18, 2010 #3
    Re: Welcome to PF!

    So should I still set the two things equal then substitute one of the accelerations(a2) out to find the other(a1) then use what you gave me to find the other(a2)?
  5. Jan 18, 2010 #4


    User Avatar
    Science Advisor
    Homework Helper

    Equal and opposite, yes. :smile:
  6. Jan 18, 2010 #5
    Well i solved it and it came out to be 1.79m/s2. Does it matter which of them has the negative acceleration or do both have equal positive accelerations?
  7. Jan 18, 2010 #6


    User Avatar
    Science Advisor
    Homework Helper

    hmm … well, you'd better say that one goes upward with acceleration 1.79m/s2, and the other goes downward …

    you'll have to make it clear you know which way they're going! :wink: :biggrin:
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook