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Inelastic collision: final velocity after collision

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  1. Sep 25, 2016 #1
    1. The problem statement, all variables and given/known data
    You are driving your 1000-kg car at a velocity of(19 m/s )ι^ when a 9.0-g bug splatters on your windshield. Before the collision, the bug was traveling at a velocity of (-1.5 m/s )ι^.
    What is the change in velocity of the car due to its encounter with the bug?


    2. Relevant equations
    pi = pf
    m1v1 + m2v2 = (m1 + m2)v

    3. The attempt at a solution
    i attempted to solve for the change in velocity using the equation outlined below and got answer of -3.0x10^-5. i know this answer is inncorrect but i cannot seem to locate my source of error
    Δv=(1.9x10^4)+ (-1.35x10^-2) -19 m/s
    1000 +0.009
     
  2. jcsd
  3. Sep 25, 2016 #2

    ehild

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    Bring the terms of the difference to common denominator, then 1.9x10^4 cancels, and you avoid rounding errors.
     
  4. Sep 25, 2016 #3
    i am unsure what you mean for me to do/ how to do that
     
  5. Sep 25, 2016 #4

    ehild

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    You calculate the difference ##\frac {19\cdot 1000- 1.5\cdot 0.009}{1000+0.009}-19 = \frac{19\cdot 1000- 1.5\cdot 0.009-19(1000+0.009)}{1000+0.009}##
    Expand and simplify.
     
  6. Sep 25, 2016 #5
    i got an answer of -1.8449 x10^-4
     
  7. Sep 25, 2016 #6

    ehild

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    It looks correct, but do not keep more than 3 significant digits.
     
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