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Math Help - Rotational kinematics question I'm having trouble with

  1. #1
    s3a
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    Rotational kinematics question I'm having trouble with

    Question:
    The flywheel of a steam engine runs with a constant angular speed of 158 rev/min. When steam is shut off, the friction of the bearings and the air brings the wheel to rest in 2.7 h.

    (a) What is the magnitude of the constant angular acceleration of the wheel?
    (b) How many rotations does the wheel make before coming to rest?
    (c) What is the magnitude of the tangential component of the linear acceleration of a particle that is located at a distance of 53 cm from the axis of rotation when the flywheel is turning at 79 rev/min?
    (d) What is the magnitude of the net linear acceleration of the particle in the above question?

    I only get (a) right which is 0.001702234 rad/s^2 but unfotunately I do not know the answers for the rest of them however what I did attempt the following:

    (b) 12798
    (c) (0.001702234 * (53/100)) m/s^2 and
    (d) sqrt((0.001702234 * (53/100))^2 + (2*pi*158/60 * (53/100))^2) m/s^2

    all of which are wrong. So if someone could help me solve them, it would be GREATLY appreciated!
    Thanks in advance!
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  2. #2
    MHF Contributor
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    Quote Originally Posted by s3a View Post
    Question:
    The flywheel of a steam engine runs with a constant angular speed of 158 rev/min. When steam is shut off, the friction of the bearings and the air brings the wheel to rest in 2.7 h.

    (a) What is the magnitude of the constant angular acceleration of the wheel?
    (b) How many rotations does the wheel make before coming to rest?
    (c) What is the magnitude of the tangential component of the linear acceleration of a particle that is located at a distance of 53 cm from the axis of rotation when the flywheel is turning at 79 rev/min?
    (d) What is the magnitude of the net linear acceleration of the particle in the above question?

    I only get (a) right which is 0.001702234 rad/s^2 but unfotunately I do not know the answers for the rest of them however what I did attempt the following:

    (b) 12798
    (c) (0.001702234 * (53/100)) m/s^2 and
    (d) sqrt((0.001702234 * (53/100))^2 + (2*pi*158/60 * (53/100))^2) m/s^2

    all of which are wrong. So if someone could help me solve them, it would be GREATLY appreciated!
    Thanks in advance!
    (b) and (c) are correct. a significant figure issue?

    for (d) , use 79 rpm instead of 158 and note that a_c = r\omega^2

    |a| = \sqrt{a_T^2 + a_c^2}<br />
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  3. #3
    s3a
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    It's probably a bug because several students are complaining but thanks for the confirmation. At least I know that I'm right . I also fixed (d) so thanks again.
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