Gauge pressure at the bottom of a barrel

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SUMMARY

The discussion focuses on calculating the gauge pressure at the bottom of a barrel containing a 0.110 m layer of oil with a density of 690 kg/m³, sitting atop 0.300 m of water. The correct formula used is Ptotal = Poil + Pwater, where the pressures of both fluids are summed to determine the total pressure at the bottom. A misunderstanding arose regarding the treatment of water pressure as a negation of oil pressure, which was clarified to be incorrect. The importance of accurately interpreting the problem statement was emphasized to avoid confusion.

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Of Mike and Men
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Homework Statement


A barrel contains a 0.110 m layer of oil and a density of 690 kg/m3 floating on water that is 0.300 m deep. What is the pressure at the bottom of the barrel?

Homework Equations

The Attempt at a Solution



Poil + Pwater = Ptotal

My question is why am I using this formula? I got the correct answer, but initially I wanted to treat the pressure of the water as a negation of the pressure of the oil, causing the barrel to float. So, Poil - Pwater. Is the reason for the addition because I am treating the bottom of the barrel as a point and the pressure acting on it in every direction equally and taking my gauge pressure from that exact point?

Thanks
 
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Of Mike and Men said:
My question is why am I using this formula? I got the correct answer, but initially I wanted to treat the pressure of the water as a negation of the pressure of the oil, causing the barrel to float.

My reading of the question is that both the oil and the water are in the barrel.
 
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CWatters said:
My reading of the question is that both the oil and the water are in the barrel.
Okay, thank you. I mis-read that. I was assuming the barrel was floating on the water. Paying attention to sentence structure is useful. ?:)
 

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