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Homework Help: System of particles passing over a pulley

  1. Jan 23, 2012 #1
    1. The problem statement, all variables and given/known data
    Two particles of masses m1=8 kg and m2=5 kg are connected to the two ends of a light inextensible string which passes over a fixed smooth pulley. Initially each of the two particles are held at a position which is 5 m above a horizontal ground. The objects are then released from rest. Assuming that the particles never reach the pulley, and also that the particles do not rebound when they strike the ground.(g=10m/s^2)

    a) find the tension in the string and the acceleration of each particle
    b) find the distance above the ground of the point H, the highest point reached by the 5 kg mass
    c) find the speed with which the system is jerked into motion and the impulse experienced by the string during the jerk.

    2. Relevant equations
    Newton's second law

    3. The attempt at a solution
    For part (a), I got a=(m1-m2)g/(m1+m2)=30/13, hence T=800/13
    I'm stuck at part (b) and (c) as I don't know the motion of the system after mass 1 (the heavier one) hit the ground and T becomes zero. I assume both masses stop moving at that moment, then the maximum height reached by mass 2 is 10m. Also, I'm not able to figure out what it means by 'the system is jerked into motion'. I would appreciate a reasonable explanation to this. Thanks
  2. jcsd
  3. Jan 23, 2012 #2
    I agree with your answer for the acceleration and tension and, like you, I do not understand what is meant by "jerked into motion"
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