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Average Speed/Velocity

  1. Sep 8, 2009 #1
    1. The problem statement, all variables and given/known data
    A car making a 200-km journey travels 50 km/h for the first 100 km. How fast must the car go in the second 100 km to average 60 km/h?


    2. Relevant equations
    There is the average velocity equation, and also the average speed equation.
    (delta x)/(delta t) = average velocity
    average speed = total distance/total time


    3. The attempt at a solution
    50 = 100/t
    to get the time? Do I need to do that?
    Then should I do the same for the next one?
     
  2. jcsd
  3. Sep 8, 2009 #2

    rl.bhat

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    Homework Helper

    t1 = 100/50 s
    t2 = 100/v s
    Total distance is given.
    Average velocity is given. Total time t = t1 + t2.
    Substitute these values in the relevant equation to find v.
     
  4. Sep 8, 2009 #3
    Ok, so ,
    t1 = 2s
    t2 = 100/v s

    The total distance is 200km. The average velocity for the 2nd portion is 60km/h. I do not have t2, because I don't have v. I am confizzled.
     
  5. Sep 8, 2009 #4

    rl.bhat

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    Homework Helper

    Total time t = 200m/60 km/h.
    t1 is known. Find t2. Then find v.
     
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