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Homework Help: Need help finding velocity

  1. Nov 23, 2012 #1
    The question I'm having trouble with is:
    A child of mass 28.0 kg is sliding on ice with a velocity of 2.25 m/s in the positive x direction. She is holding a 2.4 kg ball in her hand. She throws the ball straight ahead of her with a velocity of 2.70 m/s (in the x direction). What is her velocity immediately after releasing the ball?

    I think I need to get the rotational inertia for the ball to get its kinetic energy but i'm not given a radius.
  2. jcsd
  3. Nov 23, 2012 #2

    Doc Al

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    Staff: Mentor

    You won't need rotational inertia. (No reason to think rotation is involved here.)

    Instead, what physical principles might be relevant? Is anything conserved as she throws the ball?
  4. Nov 23, 2012 #3
    I think that if the mass is not given you are expected to consider only the translational K.E.

    Think about momentum!
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