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Homework Help: Newton's Law please help

  1. Sep 13, 2011 #1
    1. The problem statement, all variables and given/known data

    In a simulation of machinery at a mine site, blocks of wood were used as shown in the following experimental set-up in which the two blocks – A and B – both of mass 15 kg are joined by a string over a frictionless pulley. Block A rests on a frictionless incline of 30º. Block B is attached to the other end of the string at an angle of 40º as shown. The frictional force resisting the motion of block B is 50 N. The two blocks are then released. The site engineer has proposed the following hypothesis: “Block A will drag Block B to the left”. Confirm or refute this hypothesis
    2. Relevant equations

    I am unsure

    3. The attempt at a solution
    So this question popped up in a revision booklet i got. i know that block A will pull block B to the left because it has a frictionless surface and the pully is frictionless but i am unsure of how to prove this with equations :/ please help
  2. jcsd
  3. Sep 13, 2011 #2


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    It would help us help you if you provided a picture of the set up.
  4. Sep 14, 2011 #3
    if i understood you correctly,

    you will have to decompose the 2 weights into components parallel to the inclination of their respective ramps

    then for B, you will have to minus the friction force to find its net force along the ramp

    for A its just that component you found as it is frictionless

    so after that you will have to find the x component of both the resultant forces , A to the left, B to the right.

    their y-components don't matter

    you will find that x-component of A is larger, and hence, it would pull B towards A.
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