c1: một đoàn tàu đang chạy với vận tốc 45km/h thì hãm phanh, chuyển động thẳng chậm dần đều để vào ga . sau 3 phút thì tàu dừng lại. Tính quãng đường mà tàu đi đc trong thời gian hãm c2: hai ô tô cùng chuyển động đều trên đường thẳng, nếu 2 ô tô đi ngược chiều thì cứ 20 phút khoảng cách của chúng giảm 30km. Nếu chúng đi cùng chiều thì cứ sau 10 phút khoảng cách giưã chúng giảm 10 km. Tính vận tốc mỗi xe

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