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 massm rolls along a straight level track at 1.1 m/s and collides with an initially stationary,fully loaded boxcar of mass 3.9m.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 thecollision. With what speed was the loaded boxcar moving before thecollision if the empty one was moving at 1.1 m/s? ___m/s
In the railroad freight yard, an empty freight car of massm rolls along a straight level track at 1.1 m/s and collides with an initially stationary,fully loaded boxcar of mass 3.9m.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 thecollision. With what speed was the loaded boxcar moving before thecollision if the empty one was moving at 1.1 m/s? ___m/s

Explanation / Answer

(a) Using conservation of momentum we have                 Pi = Pf        Before collision we have             Pi = m (1.1) + 3.9m (0) = m * 1.1        After collision we have            Pf = (m + 3.9m) V        Therefore                m * 1.1 = (m +3.9m) V          1.1 = 4.9 V       ==> V = 1.1 / 4.9 = 0.2244m/s (b)    Pi = Pf    m (1.1) + 3.9m (v) = 0        ==> v = - 1.1 / 3.9                  = -0.2820 m/s

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