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Homework Help: Help with rotation about a fixed axis

  1. Nov 7, 2005 #1
    hey..i have a problem that states. a record has an angular speed of 34.6 rev/min. Find its Angular speed in rad/s.
    -so the answer is 3.623.
    The second part of the problem asks what angle, in radians, does it rotate in .717s. answers in rad.

    do you think you can help me?

    Also, i have some problems dealing with a ball at the end of the string with length 1.8m. It is in horizontal circle at constant speed. IT makes 3.4 rev/s. I need to find the period of the ball's motion, the frequency, and its angular velocity...but everything i have tryed has failed.
    I tryed 1.848 and .18726 for the period but was wrong. i tryed 5.34 and .5411 for the frequency but was wrong and the velocity i also got wrong.

    PLEASE HELP! im new
  2. jcsd
  3. Nov 7, 2005 #2

    Doc Al

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    Staff: Mentor

    What do you think the answer should be? If the angular speed is 3.623 radians/second, and the time is given as 0.717 seconds, how do you think you would get the angle in radians? (Hint: Angle is similar to distance, which equals rate X time.)

    Don't just give your answers, show how you got those answers. (Then we can see where you made a mistake.) Here's a hint: I assume you know that period means the time for one revolution. If you know that 3.4 revolutions takes 1 second, how long will 1 revolution take?
  4. Nov 7, 2005 #3


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    Homework Helper

    It has an angular velocity of 3.623 rad/sec. that means that,

    in 1 sec it travels through an angle of 3.623 radians
    so, in 0.717 secs it travels through an angle of ???

    For the 2nd problem, convert your angular velocity from rev/s to rad/s :smile:
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