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Dynamics A Level Questions

  1. Feb 7, 2012 #1
    1. The problem statement, all variables and given/known data
    A crane has a maximum safe working load of 1.2 * 10^4 N and is used to lift a concrete block of mass 1000kg. What is the maximum safe upward acceleration of the block while being lifted?


    2. Relevant equations
    F=ma


    3. The attempt at a solution
    F=mα
    1.2*10^4=1000*α
    α= 12m/s2


    The answer is 2.2 m/s2
     
    Last edited: Feb 7, 2012
  2. jcsd
  3. Feb 7, 2012 #2

    PeterO

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    Homework Helper

    You seem to have forgotten that while the crane is pulling up, gravity is pulling down, so the net force is much less than 1.2*10^4 N
    Acceleration is the result of the net force.
     
  4. Feb 7, 2012 #3
    Oh! I got it. Here is the solution. Is it right?

    F-f=ma
    (1.2*10^4)-(9.81*1000)=1000*a
    2190=1000a
    a=2.19
    =2.2 ms-2
     
  5. Feb 7, 2012 #4

    PeterO

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    Homework Helper

    That's more like it.
     
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