Answer:
vf = vâ/3 + 2vâ/3
Explanation:
Using the law of conservation of linear momentum,
momentum before impact = momentum after impact
So, Mvâ + 2Mvâ = 3Mv (since the railroad cars combine) where vâ = initial velocity of first railroad car, vâ = initial velocity of the other two coupled railroad cars, and vf = final velocity of the three railroad cars after impact.
Mvâ + 2Mvâ = 3Mvf
dividing through by 3M, we have
vâ/3 + 2vâ/3 = vf
vf = vâ/3 + 2vâ/3