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Tension question! Help, this homework is due midnight tonight!

  1. Oct 1, 2007 #1
    1. The problem statement, all variables and given/known data
    Ok. Well, my physics teacher has no idea what he's doing, so basically i'm lost too. This problem shouldn't be as hard as I'm making it, so obviously I'm overlooking something.

    An elevator starts from rest with a constant upward acceleration and moves 1 m in the first 2 s. A passenger in the elevator is holding a 3.3 kg bundle at the end of a vertical cord. What is the tension in the cord as the elevator accelerates?

    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Oct 1, 2007 #2

    berkeman

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    Staff: Mentor

    Welcome to the PF, pinkpanda02. First, we don't give out answers here on the PF. You are required to show your work first, and then we can offer tutorial advice to help you figure out the problem on your own. Second, we would encourage you to not wait until the last minute before asking for homework help. But that's probably pretty obvious to you right now.

    Now, what are the kinematic equations of motion, and how do they apply to this problem? The acceleration of gravity and the acceleration of this elevator are constant, so you can use the simple algebraic forms of the kinematic equations of motion. Please list them, and start to describe how you would set up an equation to figure out the answer....
     
  4. Oct 1, 2007 #3

    berkeman

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    Staff: Mentor

  5. Oct 1, 2007 #4
    But see, this is the problem. I'm not sure what to do. My teacher doesn't explain this stuff to us at all. I asked him for help, and he even got the wrong answer! I just need to know how to solve it. No equations, just what to do. I certainly don't want the ansswer. I wouldn't learn if you gave it to me. :rolleyes:
     
  6. Oct 2, 2007 #5

    berkeman

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    Staff: Mentor

    From the elevator movement of 1m in the first 2 seconds, you calculate the upward acceleration of the car. Quiz Question -- which of the kinematic equations that I linked for you is the correct one to use?

    And then you just add this acceleration to the acceleration of gravity (Quiz Question -- what is the value of the acceleration of gravity, commonly designated as "g"?), to get the total acceleration acting on the mass. Then use F=ma to calculate the total force. Please show your work if you have follow-up questions.
     
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