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Average Speed = distance/time question.

  1. Jul 5, 2009 #1
    1. The problem statement, all variables and given/known data
    A race car races on a circular racetrack of radius (r).
    (a) Write an equation for the car’s average speed when it travels a complete lap in time (t).
    (b) The radius of the track is 400m and the time to make a lap is 40s. Show that the average speed around the track is 63m/s.

    2. Relevant equations
    Average Speed = Total Distance/ Travel Time

    3. The attempt at a solution
    (a) speed = distance/time ?

    (b) 400m x 3.14 = 1256m.
    63m/s = 1256m/40s.. this is where I get lost. This obviously isn't right. I'm getting an average speed of 31.4m/s.
     
  2. jcsd
  3. Jul 5, 2009 #2

    negitron

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    400m x 3.14 = 1256m is not quite right. What's the formula for circumference again?
     
  4. Jul 5, 2009 #3
    3. The attempt at a solution
    (a) speed = distance/time ?

    (b) 400m x 2 = 800m = diameter
    800m x 3.14 = 2512 = distance
    63m/s = 2512m/40s = 62.8m/s
     
    Last edited: Jul 5, 2009
  5. Jul 5, 2009 #4
    Ty again!

    It's been awhile ;(
     
  6. Jul 5, 2009 #5

    negitron

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    Science Advisor

    Yes, you have it now.
     
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