A double bottom tank measures 25m x20m x 2m. Find the thrust on the tank top when pressed upto a head 16m of SW. Also find the resultant thrust on the tank bottom, and the direction that it acts, if the ship’s draft in SW is 10m.

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Solution :

Volume of  tank  = (L X B X H)
                         = (25m x 20m x 2m)

ans 10

Area    =     (25 x20)
          =   500m2

Pressure = (depth x density)
                = (16 x 1.025)
                =16.4  t/m2

Thrust on tank top  = (PX A)
                                      = (16.4 X 500)
                                     = 8200 t

Pressure on the tank bottom = (depth x density)
                                                            = (18 x1.025)              = 8.45t/m2

Thrust   act  on the tank bottom = (P X A)
                                                               =   (500 x 18 .45)
                                                               = 9225t

Pressure act on outside of the tank bottom = (depth x density)
                                                                            = (10 x 1.025)
                                                                           = 10.25t

Hence, Thrust acting = (P X A)
                                 = (10.25 X500)
                                 = 5125 tonnes.

Finally, Resultant thrust = (9225 -5125)
                                    = 4100 tonnes.

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