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Homework Help: Equations of motions, revolutions of turntable

  1. Oct 18, 2007 #1
    1. The problem statement, all variables and given/known data

    A turntable reaches an angular speed of 45.0 rpm, in 2.1 s, starting from rest.

    (a) Assuming the angular acceleration is constant, what is its magnitude?
    (b) How many revolutions does the turntable make during this time interval?
    ______ rev

    2. Relevant equations

    3. The attempt at a solution

    I am having trouble with the second part. I figured out magnatude of the angular acceleration but I dont remember how to find the revolutions. Anyone help?
  2. jcsd
  3. Oct 18, 2007 #2
    45RPM = 45 revolutions per minute. It seems that the question is asking you to find out how many revolutions the turntable makes in 2.1 seconds.
  4. Oct 18, 2007 #3
    rpm stands for revolutions per minute right?
  5. Oct 18, 2007 #4
  6. Oct 18, 2007 #5
    Yea RPM means revolutions per minute...but I broke it up into Rev/s and I still couldnt find the right answer. What do I do? any tips?
  7. Oct 18, 2007 #6


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    Homework Helper

    Think of angular velocity and acceleration, the same way as velocities when you do kinemtics problems.

    For example in kinematics we have:

    d = [(v1+v2)/2]*t

    here we have:

    angle traversed = [(w1 + w2)/2]*t

    here w1 = 0. w2 is 45.0 rpm in rad/s. and you have time.

    once you have the angle, you can get the number of revolutions.
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