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Angular motion homework problem

  1. Nov 2, 2009 #1
    1. The problem statement, all variables and given/known data

    An electric motor rotating a workshop grinding wheel at a rate of 90 rev/min is switched off. Assume constant negative angular acceleration of magnitude 2.50 rad/s2.
    (a) How long does it take for the grinding wheel to stop?

    (b) Through how many radians has the wheel turned during the interval found in (a)?

    2. Relevant equations
    wf=wi+at^s
    theta= 1/2 (wi+wf)t
    3. The attempt at a solution
    I got the right answer for (a) which was 3.77 sec so for (b) I thought that all you needed to do was plug in the values into the second equation to get theta but the answer I got was wrong. I got -17.766.....I don't know what I'm doing wrong...any help would be appreciated.
     
  2. jcsd
  3. Nov 2, 2009 #2
    uuh lol never mind i just had an extra negative sign
     
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