Physics Help Forum resisting force at a clasp

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 Jan 2nd 2019, 12:42 PM #1 Junior Member   Join Date: Jan 2018 Posts: 5 resisting force at a clasp Hello, 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. ANSWER: Here force along depth of A is varying continuously, so there are 3 forces on tank side. H=0.5 L=1 W= 0.5 A=0.5m2 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 =0.04 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 )
 Jan 2nd 2019, 07:30 PM #2 Senior Member   Join Date: Apr 2017 Posts: 513 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 ! topsquark likes this. Last edited by oz93666; Jan 2nd 2019 at 07:49 PM.
 Apr 25th 2019, 01:51 PM #3 Junior Member   Join Date: Apr 2019 Posts: 1 hi, 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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