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Centre of mass and translational motion

  1. Nov 16, 2008 #1
    1. The problem statement, all variables and given/known data

    A 270 kg flatcar 20 m long is moving with a speed of 5.0 m/s along horizontal frictionless rails. A 90 kg worker starts walking from one end of the car to the other in the direction of motion, with speed 3.0 m/s with respect to the car.

    2. Relevant equations

    MVcm = m1v1 + m2v2

    3. The attempt at a solution

    I found the Vcm to be 4.5 m/s

    I have no idea how to find the distance traveled by the car...can someone please help me
     
  2. jcsd
  3. Nov 16, 2008 #2

    Doc Al

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    Staff: Mentor

    How did you come up with that? (Hint: You are told that the initial speed of everything is 5.0 m/s.)
     
  4. Nov 16, 2008 #3
    I used the equation to find that...i dunno if its right or wrong..i dunno how to approach the problem
     
  5. Nov 16, 2008 #4

    Doc Al

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    Staff: Mentor

    The speed of the center of mass is given as 5.0 m/s. Since Vcm can't change, use that equation to figure out the speed of the car while the man is walking. Hint: If the speed of the car with respect to the ground is called +V, and the speed of the man with respect to the car is -3 m/s, what would be the speed of the man with respect to the ground in terms of V?
     
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