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31. Train A is initially traveling east with speed 10 m/s, slowing down with acceleration 5 m/s2. Train B is initially at rest a distance of 200 m from train A's starting location. Train B speeds up to the west with identical acceleration 5 m/s2 How long does it take for the trains to pass each d other? (A) 80 s (B) 5 s (C) 40 s (D) 10 s (E) 20 s