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How long will it take to come to rest?

  1. Dec 18, 2008 #1
    1. The problem statement, all variables and given/known data

    A steam engine is running at 200 RPM whe nits steam is shut off. The friction of its various parts produces torques that combine to decelerate the machine at 5.0 rad/s^2. How long will it take to come to rest?

    Please help asap I have a test tomorrow.

    2. Relevant equations



    3. The attempt at a solution

    [​IMG]
     
  2. jcsd
  3. Dec 18, 2008 #2

    hage567

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    You are using the right equation. Note that the angular acceleration is negative, since the steam engine is coming to rest.
     
  4. Dec 18, 2008 #3
    THanks but how do I finish it??
     
  5. Dec 18, 2008 #4

    hage567

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    Solve for t. Are you having trouble with the algebra?
     
  6. Dec 18, 2008 #5
    0 rad/s / 25.94t = 0 and that is not right
     
  7. Dec 18, 2008 #6

    hage567

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    No, that won't work.

    The equation initially is

    ωf = ωi + αt

    So you have come to the point where you have

    0 = 20.94 - 5t

    You want to get t on its own on one side of the equation. So the first step is to subtract 20.94 from both sides of the equation (whatever you do to one side you must also do it to the other side). When you do that, what do you get?
     
  8. Dec 18, 2008 #7
    THank you I got the answer now. I forgot that the 20.94 needs to go on the other side of the = in order to get t alone. THanks again
     
  9. Dec 18, 2008 #8

    hage567

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    :smile:You're welcome.
     
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