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Homework Help: Displacement & Average Velocity

  1. Sep 4, 2012 #1
    1. The problem statement, all variables and given/known data

    A car travels in a straight line at 40 km/hr for 1 h and 60 km/hr for 2 h. A) How far does it travel? B) Find the average velocity.

    2. Relevant equations

    Average velocity = Δx/Δt (change in distance/change in time)

    3. The attempt at a solution

    In solving for A, I got (1 h x 40 m/hr + 2 h x 60 km/hr) = 160 km/hr

    For B, this is where I'm confused. I know that if I try to arrange it as suggested in the formula (160 km/hr/2-1 h), wouldn't this just leave me with the remaining distance and eliminating the unit for time? Or would that be correct? I feel like it would not be though as the formula suggests, average velocity is defined by change in distance per change in time. Any help is greatly appreciated!
  2. jcsd
  3. Sep 4, 2012 #2


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    The answer to A should have units of distance, not speed.
  4. Sep 4, 2012 #3
    Oh wow, I can't believe I missed that...Thanks a lot!!!
  5. Sep 4, 2012 #4


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    average velocity is total displacement divided by total time. The total distance divided by the total time is the average speed. Doesn't make any difference in this example, though.
    right number, wrong units. You are solving for a distance.
    check units! and welcome to PF!
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