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Calculating acceleration - Quick question

  1. Sep 30, 2011 #1
    Calculating acceleration - Quick question!!!

    1. The problem statement, all variables and given/known data

    A crane if lifting 2 blocks connected to each other. both blocks weight a total of 110 kg - the crane is lifting with a force of 1500 N.

    What is the acceleration? What formula do I use? I thought I needed a time variable to calculate acceleration????

    Thanks!

    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Sep 30, 2011 #2
    Re: Calculating acceleration - Quick question!!!

    Hi nukeman, it would help you to write down relevant equations. Ignoring the detail, you have a force acting on a mass, Newtons second law will help you here.

    Cheers
     
  4. Sep 30, 2011 #3
    Re: Calculating acceleration - Quick question!!!

    So would it be acceleration = Fnet / mass?

    So, 1500 / 110 ? or making converting the KG to N,

    1500 / 1079 = 1.39 ??
     
    Last edited: Sep 30, 2011
  5. Sep 30, 2011 #4
    Re: Calculating acceleration - Quick question!!!

    can anyone confirm my answers for me? :)

    And, if I want to get the tension between the 2 blocks, I treat the bottom block as the system, and apply newtons 2nd law to it?

    So, the bottom block is 50kg, and my (hopefully correct) acceleration as in the post above is 1.39,

    tension would be 50kg / 1.39 to give me 35.97 N??
     
  6. Sep 30, 2011 #5
    Re: Calculating acceleration - Quick question!!!

    Hi, for the first question:

    Yes you are correct
    [itex] F_{net}=m a \Rightarrow a=\frac{F_{net}}{m}[/itex]
    Okay so the mass is 110kg, and the total force is 1500N.

    I do not understand what you mean by "converting" from Kg to N: Kg are units of mass, and N (Newtons) are units of Force, if it helps acceleration has units [itex] m/s^2 [/itex].

    So the correct value should be 1500/110= 13.6 m/s^2

    For the second part I am not sure exactly what you mean, a force diagram will confirm the tension between the blocks.
     
  7. Sep 30, 2011 #6
    Re: Calculating acceleration - Quick question!!!

    Isn't this "crane ... lifting" here on the Earth? So you need to account for the force of gravity as well.
     
  8. Sep 30, 2011 #7
    Re: Calculating acceleration - Quick question!!!

    "weight" generally means mass*gravity. Otherwise, they would have said "mass". So, the net force on the blocks should be weight (mass * gravity) and the force on the other side (the crane).

    Won't one of these forces overcome the other? If so, which one? This will give you a net force (mass * acceleration). You know the mass already, the acceleration should be easy to get using algebra.
     
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