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Velocity questions

  1. Jun 16, 2014 #1
    I really confused by the following:

    The distance between two black lines is 2 metres.
    The car passed 8 lines, and it uses 0.4 seconds
    such that: Ω represents the car.
    _____Ω_____<--- after
    _____Ω_____<----- before

    Is the velocity of the car 7*2/0.4= 35 ms-1 ??
    Besides, can I say that the assumption behind is that the car is moving at constant velocity?
    If not, what is the assumption?

  2. jcsd
  3. Jun 16, 2014 #2


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    Gold Member

    What is the full question given?

    (You should have actually posted this on the homework section)
  4. Jun 16, 2014 #3
    velocity of the car and the assumption behind.
  5. Jun 16, 2014 #4
    The black lines represent some lines on the road
  6. Jun 16, 2014 #5


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    If you continue refusing to state the whole problem, as given, it is impossible to help you. So far you have said that the problem is to find the velocity and that the velocity was given!
  7. Jun 16, 2014 #6
    I want to ask the assumption actually
  8. Jun 16, 2014 #7


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    Is this a language problem? I don't know how you "question the assumption" and I am still not sure what "assumption" you are talking about. Are you told that the speed is constant or are you assuming that? Are you asked to find the speed or are you given that?
  9. Jun 17, 2014 #8
    I am asked to find the velocity and based on what assumption to find the velocity.

    Cant you get that?
  10. Jun 17, 2014 #9
    Also, I want to say that the velocity is not given in the question. See it carefully before you say that....... I asked whether the velocity is 35 or not.

    Get that??
  11. Jun 17, 2014 #10
    You should be more clear in stating your question.

    From what I understand, you are asking: if a car moves 7 blocks, each of 2m length in total 0.4s then what is the average velocity of the car?
    If my interpretation of your questions is ok and the way you drew the initial and final position of the car, the displacement is 7*2m in 0.4s. Then your answer 35m/s is correct (average velocity).
    Last edited: Jun 17, 2014
  12. Jun 17, 2014 #11
    I guess your second question is, if the average velocity of the car is 35m/s then under what assumption is it true?
    The important thing to notice here is that the way you showed the initial and final position of the car, it is obvious that the whatever distance the car traveled in 0.4 s, its displacement is 14m.
    So given that diagram, we don't need any extra assumption.
  13. Jun 17, 2014 #12
    Okay, the answer is very good!! Finally, someone knows what I am trying to ask!! XDD
  14. Jun 17, 2014 #13
    Really no assumption is needed?
    But the question ask me this question ==
  15. Jun 17, 2014 #14
    Okey. Honestly it's being hard to provide help unless the complete question is stated properly. Can you restate the question exactly as it is given or upload a snapshot, maybe?

    Anyway, if the horizontal position of the car is denoted by x, then one assumption is that the initial and final position of the car have same value of x. But isn't it obvious from the diagram you drew?
  16. Jun 17, 2014 #15
    One final comment: If the instantaneous velocity of the car is also equal to 35m/s (which means that the instantaneous velocity is equal to the average velocity) then yes the car must be moving with constant velocity of magnitude 35m/s directing along the straight line from the initial to final position of the car.

    Hope this helps!
    Last edited: Jun 17, 2014
  17. Jun 17, 2014 #16
    THX Adjoint for solving the problem for me !! XDD

    so good!
  18. Jun 17, 2014 #17


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    You would have got help much sooner if you wrote the whole question.
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