Railroad car A, with mass 6275 kg, is traveling east at 6.5 m/s along a straight track. It strikes railroad car B, with mass 5155 kg, which is also traveling east along the same track at 3.8 m/s. The two railroad cars stick together. Assume the track is frictionless. How fast do the two attached railroad cars move immediately after the collision?
a. ANALYZE AND SKETCH THE PROBLEM

Knowns Unknowns

mA = vAi = = ?

mB = vBi =

B. SOLVE FOR THE UNKNOWN

Define the system

Write Pi = Pf in terms of the railroad cars’ masses and velocities.

Solve for vf