CM and Translational Motion problem

[The_Fritz]

A 280-kg flatcar 25 m long is moving with a speed of 6.0m/s along horizontal frictionless rails. A 95-kg worker starts walking from one end of the car to the other in the direction of motion, with speed 2.0m/s with respect to the car. In the time it takes for him to reach the other end, how far has the flatcar moved?


This problem falls into the category of center of mass and translational motion
M\rightarrowa_CM = \SigmaF_ext


Considering the rails are frictionless I figured both the mass of the flatcar and mass of the person were both irrelevant.
Time it takes for person to reach end of flatcar= (25m)(s/2.0m)=12.5 s
Distance traveled by flatcar = (6.0m/s)(12.5 s)= 75m
Is 75m the correct answer or am I missing a large part of this problem?

 

[member 553083]

Yes, 75 m is the correct answer. The mass of the flatcar and the worker are both irrelevant since there is no friction. The only relevant factor is the speed of the flatcar and the time it takes for the worker to walk from one end to the other.