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Homework Help: Review Q #2

  1. Sep 21, 2010 #1
    Problem solved; thanks Thaakisfox!

    1. The problem statement, all variables and given/known data
    A race car driver must average 200km/hr for six laps of the race track to qualify for a race. If he averages only 150 km/h for the first two laps, calculate the average velocity he must have over the last four laps in order to qualify.
    2. Relevant equations
    Vavg = (X2 - X1) / (T2 - T1)

    3. The attempt at a solution
    Set V average = 200 km/hr.
    200 = [150+ 4(v)]/6
    1200 = 150+4v
    1350/4 = V for last 4 laps?

    337.5 km/h per lap for the last 4 laps?
     
    Last edited: Sep 21, 2010
  2. jcsd
  3. Sep 21, 2010 #2
    You forgot to multiply the 150 with 2, as the car goes 2 laps with that speed.
     
  4. Sep 21, 2010 #3
    Alrighty. I double checked and ended up with this.

    200 km/h = [300km/h + 4(v)] / 6
    1200 = 300 +4v
    900 = 4v
    225 km/h = v per lap needed to average at 200km/h for 6 laps.

    Does that sound right?
     
  5. Sep 21, 2010 #4
    Yep thats right.
     
  6. Sep 21, 2010 #5
    Sweet! I had a feeling 337.5 was not right.
    Thanks for the help Thaakisfox!

    Problem solved!
     
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