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Hi, im having trouble finding out what formula i should use for this physics question

  1. Apr 15, 2007 #1
    1. The problem statement, all variables and given/known data
    Swati was driving her car over the speed limit when an oncoming car car flashes its lights warning her of a radar trap ahead. She decelerates from 39 m/s to 27 m/s in 6.0 s. What deceleration did her brakes apply?

    - im not sure what formula to use so does anyone have a clue what formula i could use for this question? Thanks for taking your time.:smile:
     
  2. jcsd
  3. Apr 15, 2007 #2

    cristo

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    Well, what's the definition of acceleration (or in this case deceleration) that you have come across in your lessons, or in your textbook?
     
  4. Apr 15, 2007 #3
    umm well my teacher taught us this new displacement formula but i dunt think its related to the question i need help with .. but this is the formula he taught us: d= v1 deltat+1/2 a(deltat)2 sorry i dunt kno how to make the traingle for delta and the arrow heads... im new to this
     
  5. Apr 15, 2007 #4
    but we usually use the average velocity=delta d/delta t formula..



    oh..i fthink its this formula a=delta t + v2-v1 is this correct?
     
    Last edited: Apr 15, 2007
  6. Apr 15, 2007 #5
    [tex]\[
    a = {\textstyle{{\Delta v} \over {\Delta t}}}
    \][/tex]
     
  7. Apr 15, 2007 #6
    thanks KingNothing
     
  8. Apr 15, 2007 #7
    But if i was to use a=delta v/delta t .. how do i put to veclotiys? 39 m/s to 27 m/s
     
  9. Apr 15, 2007 #8

    cristo

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    [itex]\Delta v[/itex] means "change in velocity" just like [itex]\Delta t[/itex] means change in time. Here, the change in time is 6 seconds, and the change in velocity is exactly what it sounds like it should be; namely (39-27)m/s.
     
  10. Apr 15, 2007 #9
    oh so would i just do 39-27? which is 12 m/s?
     
  11. Apr 15, 2007 #10

    cristo

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    Yup, then substitute into the equation for acceleration.
     
  12. Apr 15, 2007 #11
    Alright, thanks alot cristo for ur help and KingNothing for the formula. Thanks.
     
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