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When does change in v=v2+v1

  1. Feb 13, 2012 #1
    in this question change v=v2-v1: a car traveling at 15m/s [N] executes a gradual turn, so that it then moves at 18m/s[E]. Calcue change in veloctiy.

    but in this question change v= v2+v1: A plane's velocity changes from 200km/h[N] to 300 km/h [N 30 W]. Find the plane's change on velocity.

    How do i know when to use which formula?
     
  2. jcsd
  3. Feb 13, 2012 #2

    SammyS

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    Change in velocity is Δv = v2 - v1 . Never is v2 + v1
     
  4. Feb 14, 2012 #3
    what i mean is how do you know when to add or subtract vectors?
     
  5. Feb 14, 2012 #4

    HallsofIvy

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    The same way you know when to add or subtract numbers!
     
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