An open water tight railway wagon of mass 5 × 103 kg coasts at an initial velocity of 1.2 m/sec. without friction on a railway track. Rain falls vertically downwards into the wagon. What change then occurred in the velocity of the wagon, when it has collected 103 kg of water ?
(A) 10 m/s
(B) 3m/s
(C) 0.2m/s
(D) 9m/s
