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Average Speed/Velocity

  1. Aug 29, 2011 #1
    A honeybee leaves the hive, flies in a straight line to a flower 6 km away in 10 min, and then takes 10 minutes to return (also in a straight line).

    a.) Please find the distance travelled and displacement for the entire trip:
    distance travelled:
    I know the distance total is 12 km

    displacement: 0

    b.) Please find the average speed and average velocity for the entire trip:
    average speed:
    This is where I get confused. Total distance/rate of change in meters = Average speed. This would mean the speed is undefined.

    average velocity:
    Same confusion because the algebra would mean this question is undefined with a displacement of zero.
     
  2. jcsd
  3. Aug 29, 2011 #2
    Velocity = distance / time. As long as your time is not zero, it is defined. It's only the denominator that needs to be non-zero.

    The average speed is the total distance traveled divided by total time spent traveling.

    The velocity is similar, only it involves the total distance traveled in a direction - that is, the velocity on the way back will be the same as on the way out, only negative.
     
  4. Aug 31, 2011 #3
    Thanks for the correction. I now see that I had the formula wrong. So it is displacement over time, and time is 20 minutes. So velocity is 0/20 and speed is 12/20.
     
  5. Sep 2, 2011 #4
    That is correct, but they're funny units (kilometres per minute?).

    To change to a more physics-y, SI unit, try metres per second:

    (12km*1000 m km^-1)/(12mins*60 s min^-1)

    =12000/720= whatever it is.
     
  6. Sep 2, 2011 #5
    They do that deliberately: that is phrase the question in unweildy units, this makes you render more applicable units by the simple fact of expedience.
     
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