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Homework Help: Rotational dynamics confusion. help please

  1. Apr 11, 2008 #1
    1. Judy rides a 2m radius merry-go-round near its edge. Judy has a mass of 100 kg and the merry go round has a mass of 200 kg and rotates at 1 rad/s. What will the new angular velocity of the merry go round be if judy moves 45 percent of the way towards the center?

    2.How much tension exists in each of two cables used to lower a 10 m long, 500 kg gang plank to horizontal if the cables originate 2 meters above the planks hinges on the ship?

    3.How much electrical energy could be generated by a 672 kg super flywheel spinning at 150,000 rpm if it has a radius of 3 m and is in the shape of a disk?

    4.You want to roll a 2 m beryllium sphere 10 meters while speeding it up from rest to a velocity of 103 m/s. The density is 1848 kg/m^3

    A)How much work (NM or joules) would this take?
    B)What force would be required?
    C)How much of the force was required to do the transitional work?
    E)How long (time)

    I've used moment of intertia but I'm missing the in between steps, these have given me some trouble over the last few days
  2. jcsd
  3. Apr 11, 2008 #2
    bump. sorry if thats not allowed
  4. Apr 12, 2008 #3
    first show some attempts.
  5. Apr 13, 2008 #4
    i've been working on these today and im getting closer, i worked out the first one

    for the second one what are they referring to when they say find the tension is that just the force required or what?

    for the third when they say electrical energy do they mean gravitational potential energy? or what. because throughout this chapter and book we havent learned an electrical energy equation that relates to rotational motion

    and im still completely lost on the fourth
  6. Apr 13, 2008 #5
    for the energy of the wheel ive calucated w and I, w=15700 rad/s and I=3024, but i dont get what to do next, no other information is given so im wondering if its just an equation i need or what
  7. Apr 13, 2008 #6
    for the energy of the wheel question i used KErot. 1/2*3024*(15700)^2 and got 3.726E11 Joules, does that seem right?
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