How Do You Calculate Thrust on a Circular Trap Door Immersed in Oil?

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Discussion Overview

The discussion revolves around calculating the thrust on a circular trap door immersed in oil, specifically focusing on the application of fluid mechanics principles to determine the forces acting on the door due to the oil pressure. The context includes both theoretical calculations and practical application of formulas.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant presents a scenario involving a circular trap door with specific dimensions and fluid properties, seeking to calculate the thrust on the door.
  • Another participant suggests using the hydrostatic pressure formula P=pgh to find the pressure exerted by the oil, leading to a calculated thrust value.
  • A different calculation approach is mentioned, where the area of the door is computed using the formula for the area of a circle, contributing to a thrust calculation.
  • One participant expresses confusion over the discrepancy between their calculated thrust and the answer provided in their textbook, indicating uncertainty in their methodology.
  • A hint is provided suggesting a ratio between the calculated thrust and the textbook answer, implying a potential scaling factor in the calculations.
  • Another participant acknowledges the hint and expresses relief at the realization of the solution, indicating a moment of clarity in the discussion.

Areas of Agreement / Disagreement

The discussion reflects uncertainty and disagreement regarding the correct approach to calculating the thrust, as participants explore different methods and arrive at varying results. No consensus is reached on the correct calculation method or final answer.

Contextual Notes

Participants reference different formulas and approaches, indicating potential limitations in their understanding of fluid mechanics principles. The discussion does not resolve the discrepancies in calculated values or the assumptions underlying the calculations.

Twowaypower
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A fuel tank contains oil of a relative density of 0.7 on one side there is a circular trap door of 1.8m in diameter. The fuel level is 1.8m above the top edge of the door calculate the thrust on the door.
 
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Welcome to PF!

Hi Twowaypower! Welcome to PF! :wink:

Show us what you've tried, and where you're stuck, and then we'll know how to help! :smile:
 
I tried using
P=pgh. Which works out as 700*9.81*3.6= 24.7212kN
Then thought many had to put that int P=FA. Which as area is Pi r^2 area works out as 2.54m^2
That gave me 62.7918kN.
I have used 1/2pgbh^2 to find out thrust on submerge rectangular objects but couldn't make that one work either. The answers in my book is 47.2 kN but I just can't get it.
:/
 
Hi Twowaypower! :smile:

Hint: 47.2/62.7918 = 3/4 :wink:
 
I was scratching my head for so long and it was so obvious. Thank you. Really need that.
 

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