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Homework Help: Terminal velocity of a ping pong ball

  1. Nov 15, 2004 #1
    Hey ppl, just a quick question..

    You have a 10 g ping pong ball with a diameter of 3.5 cm...
    a)The ball is shot straight up at twice its terminal speed. What is it’s
    initial acceleration?

    i know D=W at terminal speed but when u double it do you just assume D=4D and if you do how come?

    The answer is a=-5g as summation of Fy=-D-w=-4w-w=-5mg=ma

    the -4w is just throwing me off...

    Thanks
     
  2. jcsd
  3. Nov 15, 2004 #2

    Tide

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    Science Advisor
    Homework Helper

    If [itex]v = 2 v_t[/itex] then [itex]v^2 = 4 v_t^2[/itex] which accounts for your factor of 4.
     
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