i didnt quite understand ur Q. brother....but am still jus. trying......

the net force on the water column=0.........ie forces on water column are mg, normal force exerted by the bottom of the bucket, and the force exerted by the curved surface........and im asked to find out the force exerted on the curved surface downward......=force exerted by the curved surface on the liq. column in upward dirn......

normal force at bottom=force exerted by water column on the bottom(by 3rd law)=(P+Hdg)pi*b2......here P= atmospheric pressure......

as we said net upward force on the liq. column=0

=> mg=(P+Hdg)*pi*b²+ N_y............where we are interested in finding N_y........=mg-(P+Hdg)*pi*b²........

now m cud be found out by using V*d......and finding out V in terms of a and b is the donkey work which one have to do patiently.......hope my soln. is someway related to ur Q. if not nudge me.......

rate if useful.......