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B Mechanical physics problems (step-by-step)

  1. Jan 21, 2017 #1
    I'm looking for help on a couple specific physics problems, I just need to know how to do them step by step. Feel free to answer one or both of them, any help is appreciated :)) Thanks!! :

    1) A child is sliding out of control with velocity Vc across a frozen lake. He runs head on into another child, initially at rest, with three times the mass of the first child, who holds on so that the two now slide together. What is the velocity of the couple after the collision?
    a. 2Vc
    b. Vc
    c. Vc/2
    d. Vc/3
    e. Vc/4

    2) An ice skater can rotate about a vertical axis with an angular velocity Wo by holding her arms straight out. She can then pull in her arms close to her body so that her angular velocity changes to 2Wo, without the application of any external torque. What is the ratio of her final rotational kinetic energy to her initial rotational kinetic energy?
    a. sqrt of 2
    b. 2
    c. 2(sqrt of 2)
    d. 4
    e. 8
  2. jcsd
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