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Homework Help: Did I do this angular acceleration problem right?

  1. Jun 25, 2010 #1
    The blades in a blender rotate at a rate of 7000 rpm. When the motor is turned off during operation, the blades slow to rest in 3.4 s.
    What is the angular acceleration as the blades slow down?



    Lets first convert rpm to rps and then multiply by 2π to get its angular velocity.

    7000rpm * 60 = 420000 rps * 2π = 2638937.829 rad/s

    Now just simply use.

    Wf = Wi + AT
    A = Wf - Wi / T
    A = (0) - (2638937.829) / (3.4)
    A = -776158.185 rad/s^2 <-----Answer

    The answer is negative because its decelerating.
     
  2. jcsd
  3. Jun 25, 2010 #2
    Are you sure about that?
     
  4. Jun 25, 2010 #3
    Yes you have to convert it into rps to get seconds and then multiply times 2 pie to get radians per second.
     
  5. Jun 25, 2010 #4
    1min= 60s not the other way around
     
  6. Jun 25, 2010 #5
    Calculate again. Your answer is wrong. rev convert to radian, minute convert to second.
    Unit conversion is very important. Becareful / * sign .
     
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