In the railroad freight yard, an empty freight car of mass m rolls along a strai

Question

In the railroad freight yard, an empty freight car of massmrolls along a straight level track at1.0m/s and collides with an initially stationary, fully loaded boxcar of mass4.5m. The two cars couple together upon collision. (a) What is the speed of the two cars after the collision?
m/s

(b) Suppose instead that the two cars are at rest after the collision. With what speed was the loaded boxcar moving before the collision if the empty one was moving at1.0m/s?
m/s In the railroad freight yard, an empty freight car of massmrolls along a straight level track at1.0m/s and collides with an initially stationary, fully loaded boxcar of mass4.5m. The two cars couple together upon collision. (a) What is the speed of the two cars after the collision?
m/s

(b) Suppose instead that the two cars are at rest after the collision. With what speed was the loaded boxcar moving before the collision if the empty one was moving at1.0m/s?
m/s (a) What is the speed of the two cars after the collision?
m/s

(b) Suppose instead that the two cars are at rest after the collision. With what speed was the loaded boxcar moving before the collision if the empty one was moving at1.0m/s?
m/s

Explanation / Answer

If the two cars stayed together in both problems, simply set momentum initial to momentum final in each case. Momentum, mass times velocity, is conserved in elastic collisions, such as these. A. Pi=Pf. - m*1.0+ 4.5*0 = (m+4.5)*v. Solve B. m*1.0 + 4.5*v = 0.

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