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Inelastic car collision, answers aren't matching up

  1. Sep 28, 2015 #1
    1. The problem statement, all variables and given/known data
    Car A, having a mass of 1.30 x 10+3kg is traveling at 60.0 km/h due east when it collides with car B, having a mass of mass 1.70 x 10+3kg traveling at 40.0 km/h due west. If the collision is totally inelastic, find the final velocity of car B.
    .


    2. Relevant equations
    I'm using the equation
    m1v⃗ 1+m2v⃗ 2=(m1+m2)vf

    3. The attempt at a solution
    I'm getting 146,000 = (3000)Vf which I'm then dividing to get a velocity of 48.66. But the answer key is telling me 3.33km/h due east. I haven't taken physics in years and am super rusty so any help would be much appreciated.
     
  2. jcsd
  3. Sep 28, 2015 #2

    gneill

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    Staff: Mentor

    Hi BananasAreCool, Welcome to Physics Forums.

    Did you take into account the fact that the cars are traveling in opposite directions?
     
  4. Sep 28, 2015 #3
    That's what I was thinking was the problem, what is the equation for them moving in opposite directions?
     
  5. Sep 28, 2015 #4
    I was just able to figure it out, I had to subtract instead of add the two so instead of getting 146,000 I got 10,000, which divided by 3,000 equals to 3.33km/h.
     
  6. Sep 28, 2015 #5

    gneill

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    Staff: Mentor

    Yup. Well done.
     
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