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Kinetic energy loss?

  1. Nov 2, 2011 #1
    kinetic energy loss??

    A 2850 kg car moving east at 8.0 m/s collides with a 3200 kg car moving east. The cars stick together and move east as a unit after the collision at a velocity of 4.86 m/s.
    (a) Find the velocity of the 3200 kg car before the collision.
    2.06 m/s to the east

    (b) What is the decrease in kinetic energy during the collision?

    i have tried KE=1/2mv^2 finding kinetic energy of the cars together before impact and then after

    before: 1/2(6050)(10.06^2) = 306140.89 after: 1/2(6050)(4.86^2) = 71449.29

    306140.89-71449.29 = 234691.6

    but thats not right
  2. jcsd
  3. Nov 2, 2011 #2


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    Staff: Mentor

    Re: kinetic energy loss??

    8.02 + 2.062 ≠ 10.062

    You need to find the separate KE's of the cars before collision and add them in order to find the initial KE.
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