(velocity everywhere in the smaller cross-section
Apply continuity over the same CV:
Or,
Substitute, neglecting viscous forces (friction on wall), neglecting viscous forces.
Equating, Ans.
Choice of CV is important. If CV is chosen so that the CS cuts the nozzle, then there will be reaction forces, which will be unknown:
(Fig. 14e)
; However there is no viscous force as in the previous case! Weight of the nozzle and the water inside. The latter–CV may be chosen when the question posed is: determine the force to hold the nozzle in place.
(velocity everywhere in the smaller cross-section 
neglecting viscous forces (friction on wall)
, neglecting viscous forces.
Ans.
; However there is no viscous force as in the previous case! 
Weight of the nozzle and the water inside. The latter–CV may be chosen when the question posed is: determine the force to hold the nozzle in place. 
