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Speed related to Average Velocity

  1. Jan 31, 2012 #1
    1. The problem statement, all variables and given/known data

    I am having difficulty thinking about this problem. How is speed related to average velocity?

    A car travels along a straight line at a constant speed of 47.0 mi/h for a distance d and then another distance d in the same direction at another constant speed. The average velocity for the entire trip is 33.5 mi/h.

    2. Relevant equations



    3. The attempt at a solution

    I have been trying to think of it in these terms

    (54 + Q) = 33.5

    I know this isn't right....can I get some direction

    Thanks!!!
     
  2. jcsd
  3. Jan 31, 2012 #2
    Velocity is a vector, meaning that it has a size and direction, speed is a scalar meaning that it only has a size.

    Assuming relative values , distance d is equal to distance d, your set up could be:
    (47MPH Forward + (X)MPH Forward)/2d = 33.5 Forward

    Let d be any real number, in this case the simplest number, one. you would then have:
    (47MPH Forward +(X)MPH Forward)/2 = 33.5 Forward
    (47MPH Forward +(X)MPH Forward) = 67

    Remember if it ask for a vector as a answer you MUST provide direction.

    SPOILER: Attempted Soution-
    X MPH Forward = 20
     
  4. Jan 31, 2012 #3
    Where does (54+Q) come from? This probably belongs in the relevant equations section.
    speed is a scalar quantity, average velocity is a vector
    also
    this isn't asking a clear question, despite it's presence in the problem statement
     
  5. Jan 31, 2012 #4
    I think he is solving for the second "constant speed"
     
  6. Jan 31, 2012 #5
    Such a kind person so unlike myself XD indeed it was, or seems to be, implicitly there
     
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