A man is standing on a railroad flat car that is 9.0 m long and of unknown mass The man...

A man is standing on a railroad flat car that is 9.0 m long and of unknown mass The man and the car are initially at rest on a level track (Fig. P7.74A), and the wheels of the car are frictionless. The man then runs to the opposite end of the car and the car moves a distance 1.5 m to the left (Fig. P7.74B). Estimate the mass of the car.