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Homework Help: Blocks and Newton's Laws

  1. Oct 25, 2009 #1
    1. The problem statement, all variables and given/known data
    "Blocks A, B, and C are placed as in the figure and connected by ropes of neligible mass. Both A and B weigh 25.0 N each, and the coefficient of kinetic friction between each block and the surface is 0.35. Block C descends with constant velocity. a) Draw seperate free body diagrams shwoing the forces acting on A and B. b)Find the tension in the rope connecting blocks A and B. c) What is the weight of block C? d) If the rope connecting A and B were cut, what would be the acceleration of C?"

    2. Relevant equations

    3. The attempt at a solution
    I've gotten as far as trying to find "A" :b)
    Let ' T1 ' & ' T2 ' be the tensions in the rope connecting blocks AB and BC respct.

    Apply ; Newton's 2nd Law
    Writing the equation of motion for mB
    T1 - mBg Sin 36.9 0 - mk mBg Cos 36.9 0 - T2 = mB a -----------(i)
    Writing the equation of motion for mA

    T2 - mk mA g = mA a ----------------------------(ii)
    Writing the equation of motion for mC

    mC g - T1 = mC a ----------------------------(ii)

    Add equ(i); equ (ii) & equ(iii) ; we have
    to calculate the value of a & put it in equation (i) & (ii) respt, to get the value of T1 & T 2
    >>Can't find a though :( Help! :cry:
  2. jcsd
  3. Oct 25, 2009 #2


    User Avatar
    Homework Helper

    Hi raychelle93, welcome to PF.
    Your second equation for mass A is wrong. Check it.
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