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Homework Help: Optics: What is the speed of the sprinter's image?

  1. Sep 23, 2008 #1
    1. The problem statement, all variables and given/known data
    A sports photographer has a 150 mm focal length lens on his camera. The photographer wants to photograph a sprinter running straight away from him at 5 m/s. What is the speed of the sprinter's image at the instant the sprinter is 10 m in front of the lens?

    2. Relevant equations

    3. The attempt at a solution

    Here's my best guess:

    (1/f)=(1/s')+(1/s) (1/.150m)= (1/s') + (1/10m) s'=.152, so the absolute value of the magnification is (.152/10m)= -.0152

    and (.0152)(5m/s)= .076 m/s = 76 mm/s Is this anywhere close to correct?
  2. jcsd
  3. Sep 23, 2008 #2
    Any thoughts about this one?
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