# Homework Help: Centre of mass and translational motion

1. Nov 16, 2008

### godwinscareer

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. Nov 16, 2008

### Staff: Mentor

How did you come up with that? (Hint: You are told that the initial speed of everything is 5.0 m/s.)

3. Nov 16, 2008

### godwinscareer

I used the equation to find that...i dunno if its right or wrong..i dunno how to approach the problem

4. Nov 16, 2008

### 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?