6. A 5000 kg freight car moving at 4km/hr collides and couples with an 8000 kg freight car which is initially at rest. The approximate common final speed of these two cars is
(A) 1km/h
(B) 1.3km/h
(C) 1.5km/h
(D) 2.5km/h
(A) 1km/h
(B) 1.3km/h
(C) 1.5km/h
(D) 2.5km/h