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Old Jan 2nd 2019, 12:42 PM   #1
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Join Date: Jan 2018
Posts: 5
Question resisting force at a clasp


I have the below problem followed by the answer I believe it to be. Would somebody be able to confirm I have got it right as I am not sure??

Hinged water storage is shown below. Its top side is denoted as C, the narrow side as B and the long side as A. Assume water density is 1000 kg/m3 and gravity is 9.81 m/s2 Side A is hinged at the bottom edge and secured using a clasp at its top edge. Dimensions are: L = 1m, H = 0.5m & W = 0.5m

When the tank is full of water:

a) Calculate the required resisting force at the clasp to keep the panel shut.


Here force along depth of A is varying continuously, so there are 3 forces on tank side.



W= 0.5


y =0.25

1st moment of area =

Area * y = 0.5 *0.25 = 0.125

2nd moment of area =

Iss = Iyy +A(y) 2 = BD3 /12 + BD (y)2

=1* (0.5)3 /12 + 1*0.5 *(0.25)2


Center of pressure:

= 2nd moment / 1st moment = 0.04 / 0.125 = 0.328

Total Thrust force

= ρ*g*A* y

= 1000*9.8*0.5*0.25 = 1225 N

The resisting force on the clasp F2.

Resistive Force x Distance from Hinge = Clasp Force x Distance from Hinge

F1 D1 = F2 D2

1225* 0.3 = F2 *0.5

F2 =1225* 0.3 / 0.5

=735 N

( F3 is the Hinge Force = F2 - F1 =1225 -735 = 490 N )
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Old Jan 2nd 2019, 07:30 PM   #2
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The tank side is 0.5 x 1 .......total area 0.5

Height of tank 0.5m .... pressure at bottom is 9.81 x 0.5 x 1000 = 4905 N/m2

Pressure at top is zero ...average pressure on side is 2452.5 N/m2

total force on side is 0.5 x 2452.5= 1226.25N

We can regard this as pushing at the center of the face...

This force acts about the hinge at the bottom , so the clasp at the top will feel half this force ..... 613.125N

Hmmm ... not sure that's correct!!

The total force on the side is correct , but where will it act??? ...closer to the bottom .... 1/3 rd up !!!

So the force acting 1/3 from bottom is 1226.25 .... force on clasp is therefore 1/3rd of that = 408.75N I think that's right !
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Last edited by oz93666; Jan 2nd 2019 at 07:49 PM.
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Old Apr 25th 2019, 01:51 PM   #3
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Did you get this right in the end? I have the same question.

I have done the same for part A

But part b the forces on hinge and clasp. I cannot find the right answer.
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  Physics Help Forum > High School and Pre-University Physics Help > Thermodynamics and Fluid Mechanics

clasp, force, resisting

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