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Homework Help: Average speed and velocity

  1. Sep 2, 2011 #1
    1. The problem statement, all variables and given/known data

    A commuting student leaves home and drives to school at an average speed of 42.0 km/h. After 22.0 min she realizes that she has forgotten her homework and returns home to get it at the same average speed. It takes 8.0 min to find the report, after which the trip to school 42.0 km away to the east is resumed at the same speed as before.
    What is the average speed for the entire trip ? What is the average velocity for the entire trip?

    2. Relevant equations

    speed av= total distance/delta t (change in t)
    v av (average velocity)=delta x/delta t (change in x, change in t)

    3. The attempt at a solution

    I've tried numerous things with no success. Please help!!!
  2. jcsd
  3. Sep 2, 2011 #2
    Remember that speed is scalar and velocity is vector. If you wall 10 meters forward and then turn back and return to your original spot then you will have traveled a total distance of 20 meters. But your total displacement is 0. Speed is associated with distance and velocity is associated with displacement.
  4. Sep 2, 2011 #3
    ok so for her total dispacement she basically only went 42 km since she had to turn around the first time correct? but im having trouble with the time would her total time be 30 mins since she had to turn around and then look for the report?
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