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Homework Help: Distance and speed

  1. Sep 8, 2009 #1
    1. The problem statement, all variables and given/known data

    A mortorist travels 80km at 100 km/h, and 50 km at 75 km/h. WHat is the average speed for the trip?

    2. Relevant equations
    I used (avg)s=distance/time

    3. The attempt at a solution
    I got 6.2 km/h which I know is way off.
  2. jcsd
  3. Sep 8, 2009 #2
    It's a good first step to realize that your answer is not terribly realistic.

    I believe you have the right equation. The average speed is: d/t. What is the total distance travel (d=???)? The little trick will be to find out how long it took the motorist to travel this distance (t=???)?

  4. Sep 8, 2009 #3
    [tex]v_{avg}=\frac{\Delta x }{\Delta t}[/tex]
    Find how far it travels in part one and add that to how far it travels in trip 2. And do the same for t.
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