Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Mechanics - Relative Tension

  1. Oct 19, 2006 #1
    http://img213.imageshack.us/img213/6969/physicsproblemhq3.png [Broken]

    A rope of negligible mass passes over a pulley of negligible mass attached to the ceiling as shown above. One end of the rope is held by Student A of mass 70 kg, who is at rest on the floor. The opposite end of the rope is held by Student B of mass 60 kg, who is suspended at rest above the floor.

    The first 2 questions asked for simple calculations, but now questions (d) and (e) ask:

    (d) As Student B is accelerating at .25 m/s^2, is Student A pulled upward off the floor? Justify your answer.

    Now I do not quite understand this..I guess it makes sense since the acceleration is so small, it doesn't have enough Fnet to make Student A go upwards. But (e) is as follows:

    With what minimum acceleration must Student B climb up the rope to lift Student A upward off the floor?

    I do not understand how to calculate this. I have the answer as 1.6 m/s^2 as per my teacher's key. If anyone could explain how to arrive at this answer please help me out! I have completed FBDs for these two Students so it would be fine to speak to me in terms of the forces. Thanks to anyone who could help me with this!
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Oct 19, 2006 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Hint: What tension is produced in the rope when Student B climbs? How much tension is needed to lift Student A?
  4. Oct 19, 2006 #3
    AH i just got it. thanks for the response, I realized ForceNET. So I took the difference of Student A's weight and the tension on Student B and got acceleration from that. Thanks.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook