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Homework Help: Acceleration of the elevator

  1. Oct 3, 2008 #1


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

    While an elevator of mass 2442 kg moves upward, the tension in the cable is 34.2 kN

    2. Relevant equations

    (a) What is the ?

    3. The attempt at a solution
    a= f/m
    a= 34200N/2442kg =14.0
  2. jcsd
  3. Oct 3, 2008 #2


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    Homework Helper

    Your answer is not correct. What is the net force? You've forgotten about gravity.
  4. Oct 3, 2008 #3
    Yes, as hage567 already said, you've forgotten about gravity.

    Any time you have a question that deals with forces, it's a really good idea to draw a free-body diagram. Draw the object as a dot and then draw arrows representing the forces on the object.

    So what would the free-body diagram look like here? You have an elevator with two forces acting on it (if we ignore friction). If we assume the elevator is travelling perpendicular to the surface of the earth, the tension force pulls straight up, and gravity pulls straight down. They have different magnitudes, however.

    How do you think you will take the force of gravity into account?

    You are right about how to calculate the acceleration once you know the net force acting on the elevator, though.
  5. Oct 4, 2008 #4


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    hey thanks guys this is first time physics really confused however I think i got the answer but still kind of wrong this is what i did 34200-2442*9.81=1024


    f/m =1024/23956 =0.42m/s^2
    the answer should be 4.2m/s^2 i know I m little off calculation what am i doing wrong
  6. Oct 5, 2008 #5
    Looks like the first thing you did wrong was that 34200-(2442*9.81)=10243.98 N, not 1024 N.

    Also, why is the mass of the elevator now 23956 kg? It should be only 2442 kg.

    So, you have (10243.98 N / 2442 kg) = 4.1949 m/s^2 or 4.2 m/s^2.

    I hope this helps.
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