UPSC NDA I 2023 General Ability Solved Paper

A railway wagon (open at the top) of mass M1 is moving with speed v1 along a straight track. As a result of rain, after some time it gets partially filled with water so that the mass of the wagon becomes M2 and speed becomes v2. Taking the rain to be falling vertically and water stationary inside the wagon, the relation between the two speeds v1 and v2 is :