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Homework Help: An Inelastic Collision Crash Course

  1. May 31, 2009 #1
    1. The problem statement, all variables and given/known data

    Three carts move on a frictionless horizontal track with different masses and speeds.

    Cart 1: 4 kg (5 m/s to the right)
    Cart 2: 10 kg (3 m/s to the right)
    Cart 3: 3 kg (4 m/s to the left)

    Cart 1 and 2 are right behind each other on the left side of the track while Cart 3 is by itself on the right side of the track.

    The carts stick together after colliding.

    Find the final velocity of the three carts. Answer in units of m/s.

    2. Relevant equations

    Inelastic collision:
    Vf = v1(i) (m1/m1 + m2)

    3. The attempt at a solution

    Since we know that the masses stick together after colliding, then we know this system is fully inelastic; therefore, we can use the above equation.

    Furthermore, we can say that Cart 1 and Cart 2 are one mass or m1 (4+10 = 14 kg) and Cart 3 is m2 (3 kg).


    Vf = v1(i) (14 kg/14 kg + 3 kg)
    vf = v1(i) (0.8235294118)

    However, I cannot figure out how to find the initial velocity of Cart 1 and 2 together.
  2. jcsd
  3. May 31, 2009 #2


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    Homework Helper

    First of all find the combined velocity of m1 and m2 using the relevant equation. To find the final velocity of all masses, use the equation for combined mass of m1 and m2 with m3.
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