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Homework Help: Can someone check if i'm doing this right?

  1. Jul 12, 2007 #1
    Dubbie is moving directly along a normal line toward a plain mirror at a speed of 3.5 m/s, what is the speed of the image relative to Dubbie?

    v Dubbie + v mirror = v image
    3.5 m/s + 3.5 m/s = 7.0 m/s

    What is the speed of the image, relative to Dubbie, if Dubbie walk away from the mirror surface at 3.5 m/s at an angle of 300 to the mirror surface?

    θ = 300
    v= 3.5 m/s

    x/v= sinθ
    x/(3.5 m/s) = sin300
    x = [(3.5 m/s) sin300]
    x = 1.75 m/s
  2. jcsd
  3. Jul 12, 2007 #2
    Sorry.. should be sin 30 deg
  4. Jul 13, 2007 #3


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    Staff Emeritus
    Science Advisor
    Gold Member

    I'm not sure what you're doing for part 2. Have you drawn a diagram of what is happening and what you need to find out? Basically you want to find the velocity normal to the surface of the mirror and double that.
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