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Lamp hanging in a elevator

  1. Dec 16, 2008 #1
    1. The problem statement, all variables and given/known data

    A 3.0-kg lamp is suspended by a wire from the ceiling of an elevator. What can you conclude about the
    tension in the wire under each of the following circumstances? (Give a numerical result, or a range of possible
    numerical results, or if you can’t conclude anything about the tension in the wire, say so explicitly. Justify your
    response in each case.)

    a. The elevator is moving downward with a constant speed of 6.0 m/s.

    b. The elevator is moving upward with speed of 6.0 m/s, and slowing down at a rate of 2.0 m/s/s.

    c. The elevator is moving downward with speed of 6.0 m/s, and slowing down at a rate of 2.0 m/s/s. (3 pts)

    2. Relevant equations

    F=ma

    3. The attempt at a solution

    a: ma=Tension-mg
    (3kg)(0m/s2)=Tension-(3kg)g
    Tension=29.4N

    b: ma=Tension-mg
    (3kg)(2m/s2)=Tension-(3kg)g
    Tension=35.4N

    c: ma=Tension-mg
    (3kg)(-2m/s2)=Tension-(3kg)g
    Tension=23.4N

    I'm not sure if I even did this right please check it out!
     
  2. jcsd
  3. Dec 16, 2008 #2

    PhanthomJay

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    Gold Member

    a looks good, but you got b and c reversed. Draw a FBD, note the direction of the acceleration, and examine the direction of the forces and net forces more closely.
     
  4. Dec 16, 2008 #3
    Oh yes I got mixed up...Thank you
     
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