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Homework Help: Rotation with a Pulley and Masses

  1. Mar 16, 2005 #1
    one block has a mass M = 500 g, the other has mass m = 460 g, and the pulley, which is mounted in horizontal frictionless bearings, has a radius of 5.00 cm. When released from rest, the heavier block falls 85.5 cm in 2.47 s (without the cord slipping on the pulley).

    First I did conversions:
    M = .5kg, m = .46 kg, r = .05 m
    fall = .855m in 2.47 s

    I am unable to do part b and c right, so I am unable to go further.
    Here is my work:

    .855m = 1/2 a (2.47^2) a = .28 m/s^2

    however, It asks for 2 tensions. I never learned how to seperate them like that, especially with a pulley. I did:

    9.8 m/s^2 * .5kg = 4.9 N
    9.8 m/s^2 * .46kg = 4.508 N

    Tension of Cord = 4.9N + 4.508N. Obviously this isn't right, where do I go from here, or did I miss something?

    (a) What is the magnitude of the block's acceleration?
    .28 m/s2
    (b) What is the tension in the part of the cord that supports the heavier block?
    (c) What is the tension in the part of the cord that supports the lighter block?
    (d) What is the magnitude of the pulley's angular acceleration?
    (e) What is its rotational inertia?
    kg ยท m2
    Last edited: Mar 16, 2005
  2. jcsd
  3. Mar 16, 2005 #2
    I got it all, thanks though
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