A non viscous liquid of constant density 500 kg/m3 flows in a variable cross-sectional tube [Fig. (6)]. The
 

area of cross section of the tube at the two points P and Q at heights of 3 m and 6 m are 2x10^-3 m³ and 4x10^-3 m³ respectively. The work done per unit
volume by the forces of gravity as fluid flows from point P to Q is

• A

  $29\cdot 4\mathrm{J}/{\mathrm{m}}^3$

• B

  $-1\cdot 47\times {10}^4\mathrm{J}/{\mathrm{m}}^3$

• C

  $-2\cdot 94\times {10}^4\mathrm{J}/{\mathrm{m}}^3$

• D

   none of these