Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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

  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
    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
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook