4. Water enters through end A with speed and leaves through end B with speed  of a cylindrical tube AB.

The tube is always completely filled with water. In case I tube is horizontal and in case II it is vertical with end A upwards and in case III it is vertical with end B We have v₁ = v₂ for

(a)  Case I                                               (b)   Case II

(c)   Case III                                            (d)   Each case

Explanation-(d) This happens in accordance with equation of continuity and this equation was derived on the principle of conservation of mass and it is true in every case, either tube remain horizontal or vertical.