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How much distance did the fly cover?

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  1. Aug 5, 2015 #1
    1. The problem statement, all variables and given/known data
    You have two cars traveling on a course to crash into each other, a fly is on one of the cars. The question is how much distance does the fly cover until the cars crash?
    V= velocity,t=time
    Df=?
    p/v1,v2
    lets say the cars are traveling at the same speed


    C1at0mw.png
    This is a sketch of the problem

    2. Relevant equations
    http://images.tutorvista.com/cms/formulaimages/83/instantaneous-velocity-formulas.PNG [Broken]


    3. The attempt at a solution
    v(t)= at + c

     
    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. Aug 5, 2015 #2

    haruspex

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    Your diagram shows three velocities. Please explain what those are and post some attempt.
     
  4. Aug 5, 2015 #3
    i have been trying to slove this thing for the past 5 hours and i dont understand one bit of it so please dont blame and me
     
  5. Aug 5, 2015 #4

    haruspex

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    Did you draw the diagram? If so, you must know what the three velocities represent.
    Are you sure you've left nothing out? If you haven't, why would the distance the fly travels be any different from the distance the car it is on travels?
     
  6. Aug 5, 2015 #5
    My teacher drew this diagram ( it was the only thing that was on the board for hw) and the he did not say what any of the variables were,so i just said 10 so i could understand the problem better but i had no luck
     
  7. Aug 5, 2015 #6

    berkeman

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    With the hints I've been giving you via PM, you really need to write out the 2 equations I suggested and start trying to solve for the time when the 2 cars meet.
     
  8. Aug 5, 2015 #7

    berkeman

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    What is the equation for the distance an object travels given its velocity and the time? Include units in your equation.

    Use that form of equation to write the two equations of motion for the two cars. Call it the x-axis, with the left car starting at x=0 and the right car starting at x=d.
     
  9. Aug 5, 2015 #8
    average acceleration = (x-0 units/t seconds)
    average acceleration= ( x-d units/t seconds)
    ((x-0 units/t seconds)=( x-d units/t seconds)
     
    Last edited: Aug 5, 2015
  10. Aug 5, 2015 #9

    berkeman

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    No, there is no acceleration in this problem as stated. V2 and V3 are constant until the cars meet, right?

    The units of distance are meters [m]. The units of velocity are meters per second [m/s]. The units of time are seconds [ s ]

    When you write an equation, the units of the lefthand side (LHS) must equal the units of the RHS. So what is the equation relating distance, velocity and time?
     
  11. Aug 5, 2015 #10
    d=1/2(v2+v3)t
     
  12. Aug 5, 2015 #11
    Could this be the following puzzle?:

    Two cars with velocities v1 and v2 are on a straight collision course a distance d apart. A fly on one of the cars flies toward the other at velocity v3 which is greater than either of the car's velocities. Upon reaching the other car, the fly instantly turns around and heads back toward the previous car. This repeats until the cars collide. What is the total distance the fly flies before the cars collide?
     
  13. Aug 5, 2015 #12
    yes yes that is what that problem is ,but i dont know how to slove it
     
  14. Aug 5, 2015 #13
    Why the 1/2?

    And why the v3 and not v1?
     
  15. Aug 5, 2015 #14
    because i dont know what i am doing and now that i look at it v1 is what fits. I got that 1/2 form this formula eqn_displacement3.jpg
     
  16. Aug 5, 2015 #15
    OK, so what's the time before the cars collide?
     
  17. Aug 5, 2015 #16
    dont know,the teacher didnt say,so do i need to know the time to slove this problem
     
  18. Aug 5, 2015 #17
    Well, if you have two cars heading toward each other at v1 and v2, starting a distance d apart, how long before they collide? Not the number, the equation t = ..........
     
  19. Aug 5, 2015 #18
    time = distance / speed,both of which i dont know
     
  20. Aug 5, 2015 #19
    You have the distance d. You have the closing speed v1+v2, so write the equation.
     
  21. Aug 5, 2015 #20
    t=d/v1+v2
     
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