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Homework Help: Can a person hanging from a rope pull the person holding the rope up?

  1. Jan 11, 2012 #1
    1. The problem statement, all variables and given/known data

    A rope of negligible mass passes over a pulley of negligible mass attached to the ceiling. One end is held by student A (70 kg) who is at rest. The other side has student b (60 kg).

    I need to explain why or why not student b can lift student a off of the ground if he accelerates up the rope, increasing tension.

    2. Relevant equations

    the force of student A is 700 N (70kg x 10 m/s^2)
    the force of student B is 600 N (60kg x 10m/s^2)
    the normal force exerted on student A by the floor is 100N (?)
    the force of tension will vary depending on student B's acceleration (F=ma)

    3. The attempt at a solution

    I don't believe that it would be possible to pull the person holding the rope up, but i'm not sure how to prove it.
  2. jcsd
  3. Jan 11, 2012 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Hello patriots51. Welcome to PF !

    If you were told that it is possible for student B to lift student A off of the ground, could you explain how it's possible?
  4. Jan 12, 2012 #3


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    Staff: Mentor

    To demonstrate "lifting off the ground" B just needs to momentarily cause A's feet leave the floor.
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