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Average speed

  1. Sep 4, 2015 #1
    1. The problem statement, all variables and given/known data
    A racing car accelerates uniformly through three gears, changes with the following average speed
    20 for 2.0 s
    40 for 2.0 s
    60 for 6.0 s
    what is the overall average speed of the car?
    a) 12
    b) 13.3
    c) 40
    d) 48
    e) 37
    2. Relevant equations


    3. The attempt at a solution
     
  2. jcsd
  3. Sep 4, 2015 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Well? Where's your attempt?
     
  4. Sep 4, 2015 #3
    could not think of a possible formula.
     
  5. Sep 4, 2015 #4

    Doc Al

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    Staff: Mentor

    What's the most basic definition of average speed?
     
  6. Sep 4, 2015 #5
    distance traveled by an object during an interval
     
  7. Sep 4, 2015 #6
    err, everybody in the whole world knows that

    speed = miles per hour (or km per hour)

    so you know one formula!
     
  8. Sep 4, 2015 #7
    but in the case of above mentioned question three speeds and vales of time are give...not distance and time....i have to drive average speed using 3 vales of speed and time
     
  9. Sep 4, 2015 #8
    okay
    you are in a car that goes 20 miles per hour for 2 hours; then 40 miles per hour for 2 hours and then 60 miles an hour for 6 hours.

    how long has elapsed (in hours) and how far has the car gone (in miles) ?
     
  10. Sep 4, 2015 #9
    could it be done in a way that i first find out 3 values of distance( x= vt) using the above data and then taking 10 s as total time I find average speed?
     
  11. Sep 4, 2015 #10
    Q1) a car travels at 20mph for 2 hours. How far has it gone?
     
  12. Sep 4, 2015 #11
    40 miles
     
  13. Sep 4, 2015 #12
    it would be 480 miles in total
     
  14. Sep 4, 2015 #13
    edit, you know how to do it now.
     
  15. Sep 4, 2015 #14
    are you referring to this
    "could it be done in a way that i first find out 3 values of distance( x= vt) using the above data and then taking 10 s as total time I find average speed?"
     
  16. Sep 4, 2015 #15
    I'm referring to the fact you now know the total distance and the total time so you know the speed.

    Don't overcomplicate this!
     
  17. Sep 4, 2015 #16

    Doc Al

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    Staff: Mentor

    Exactly!

    Just calculate the total distance traveled.
     
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