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!

3 Blocks Create a Tension Force- Find Acceleration

  1. Oct 4, 2008 #1
    1. The problem statement, all variables and given/known data
    The coefficient of kinetic friction between the m = 2.6 kg block in Figure P8.35 and the table is 0.28. What is the acceleration of the 2.6 kg block? (The image is attached)

    2. Relevant equations

    Fk= (Mu)(N)
    2nd Law statements

    3. The attempt at a solution
    I began by drawing three force diagrams, one for each block. Using the 2.6 and 3 blocks I wrote out 2nd law statements (because the block is shifting right), and substituted in variables for the friction forece equation:

    Ca= T- Cg
    Ba= T- Fk
    Fk=(Mu)(Bg).... (According to my force diagrams , normal force equals weight force)

    Then I sovled for T on the first equation. Substituting that in for T in the second, and replacing the Fk with the other equation:

    Ba= Ca+ Cg- (Mu)(Bg)

    I then solved for a. After plugging in all the numbers, I got a very high number as my a. Near 55, if I recall. What exactly did I do wrong?

    Attached Files:

  2. jcsd
  3. Oct 5, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor

    The tension is different for each rope. (If not, there would be no net force on the middle block.)
  4. Oct 5, 2008 #3
    But, according to the 3rd law, the tension between the 3 block and the 2.6 block would be equal. So why would the substitution not work?

    Thanks in advance!
  5. Oct 5, 2008 #4

    Doc Al

    User Avatar

    Staff: Mentor

    Right, I misinterpreted what T you were talking about.
    Because there are two tension forces on the middle block.

    You left out one of the tension forces.
  6. Oct 5, 2008 #5
    Right. That makes sense. I suppose I'm thinking horizontally (a different problem I had to do). Thank you! Now, is it possible to include the third equation? Or should I just do the two separately. My fear is that the accelerations won't equal. I'll try it out right now.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?