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Homework Help: Angular Velocity and Acceleration for Elevator Mechanism

  1. Apr 24, 2015 #1
    1. The problem statement, all variables and given/known data
    In a charming 19th-century hotel, an old-style elevator is connected to a counterweight by a cable that passes over a rotating disk 3.50m in diameter (the figure (Figure 1) ). The elevator is raised and lowered by turning the disk, and the cable does not slip on the rim of the disk but turns with it.

    a) At how many rpm must the disk turn to raise the elevator at 15.0cm/s ?

    b) To start the elevator moving, it must be accelerated at 1/8g. What must be the angular acceleration of the disk, in rad/s^2?

    c) Through what angle (in radians ) has the disk turned when it has raised the elevator 3.10m between floors?

    d) Through what angle (in degrees ) has the disk turned when it has raised the elevator 3.10m between floors?

    2. Relevant equations
    E = (1/2)Iw^(2)
    I = (1/2)mR^(2)
    w = v/R

    3. The attempt at a solution
    I tried using w = v/R but it didn't work! I even converted it to rpm but got the wrong answer!

    Attached Files:

  2. jcsd
  3. Apr 24, 2015 #2
    Post your work, please. Keep in mind that rpm is revolutions per minute. The velocity you are given is in cm/s.
  4. Apr 24, 2015 #3
    I made a calculation mistake! The answer is 0.82 rpm
  5. Apr 24, 2015 #4


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    So is this thread done, or do you still have questions?
  6. Apr 24, 2015 #5
    It's done :D
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