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Motion & Forces Problem

  1. Oct 26, 2009 #1
    1. The problem statement, all variables and given/known data

    Two identical blocks A & B each of mass, m, are connected together by a light string, S1, and are placed on a smooth plane inclined at 30degrees to the hotizontal. A second string, S2, is attached to block A and is used to tow the blocks up the slope with S2 inclined at 30degress to the slope.

    a) Show that if block A is to remain in contact with the slope, the tension in S2 cannot exceed mg.sqrt3 and hence find the maximum possible acceleration of the system.

    b) Show that the ration between the tensions in S1 and S2 is sqrt3 : 4, independent of the acceleration of the system

    2. Relevant equations
    All the equation you may need to use

    3. The attempt at a solution
    Dont know where to start from. When the questions states if block A needs to remain in contact.. its confusing me.
  2. jcsd
  3. Oct 26, 2009 #2


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    Homework Helper

    The thing is that the string is at an angle to the slope and thus tends to lift block A off the slope. You'll have to find the normal force(s) and find the value of the string force that makes the total normal force zero (liftoff).
  4. Oct 26, 2009 #3
    i know the principle, i just cant come to prove it... if anyone can show me the first lines.
  5. Oct 26, 2009 #4


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    Homework Helper

    Can you find the component of mg that is normal - straight into the slope? Then do the same for the string force. If you can't see it, draw a diagram and show the forces separated into normal and parallel to the ramp components.
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