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F=ma, Suspended masses

  1. Nov 21, 2008 #1
    1. The problem statement, all variables and given/known data
    A mass of 1kg is suspended from a 50N spring balance, and then a thread from the first mass suspends a further mass of 2kg. The thread is then burned through. What is the acceleration of each mass at the instant the thread snaps?

    2. Relevant equations
    F=ma

    3. The attempt at a solution
    Well the problem is that I don't understand the question; I am not sure how to include the 50N.
    Can someone reword the question for me so that it is more understandable?

    At the moment I'm thinking F=(3g+50/g)+(3+50/g)a
     
  2. jcsd
  3. Nov 21, 2008 #2
    I think the 50N is mentioned to tell you that the spring is capable of suspending the two masses, and to spring back if the mass at the bottom is suddenly detached.

    Before the thread is burnt, the spring is exerting the required to lift both masses against gravity. When the thread is burnt, the spring would suddenly yank the mass on top upward. The question is asking for the accelerations of the two masses in that instance.

    If the question did not mention that the spring is 50N, and the spring was only 5N, then even if the thread is burnt, the load on top would not move because the spring itself is not strong enough to lift it.
     
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