Pressure question. (TPRH Science Workbook)

[ManOfDiligence]

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The question states:

Which of the following best relates the pressures at each of the cross sections A, B, and C?

I thought the answer would be B, since pressure is measured as = p(density)g(10)y(height). The lower the point, the lower the pressure...no? Am I using the wrong pressure formula here?

Thank you in advance.

 

[brood910]

You didnt provide us with full information given.
You should realize that y in pgy is the distance between interfaces of two fluids with different densities.
So, that's when your logic works. So, if A, B, and C have different densities, it's a different story.

 

[ManOfDiligence]

This is the relevant info in the passage.

 

[stickywebz]

since this is dealing with atmospheric pressure there's less air molecules higher up so therefore the pressure will be lower the higher you go

 

[siffster]

I just looked over this passage, so I will give my take on it. The passage says that the pole obeys Hooke's law. so basically, if you were to put something on top of the pole, the pole will be compressed. The sigma sign is referred to the stress applied to the pole(that is, the force applied to the top of the pole in order to compress it by some amount). That said, the force required to compress the pole from the top to point C is less than the force required to compress the pole from the top to point B, right? Therefore, the stress required to compress the pole from the top to point A is the greatest. That was my first thought when reading this passage.

I'm guessing you could follow the equations given too. so they give you P=pgh. But they also say that h is the height ABOVE a given point(from the top to the point of interest). Therefore, the h-value for A is the height of the entire pole, while the h-value for point C is one-third the height of the entire pole.

The pressure at each point is due to the weight of the pole pushing down. At point C, only one-third of the pole is pushing down. at point b, its two-thirds of the pole, and at point A, the weight of the entire pole is pushing down. Thus, you can see how the pressure at point A is highest because you have the entire pole pushing down at that point.

Sorry if I confused you even more hehe

 

[dyspareunia]

View attachment 179055

The question states:

Which of the following best relates the pressures at each of the cross sections A, B, and C?

I thought the answer would be B, since pressure is measured as = p(density)g(10)y(height). The lower the point, the lower the pressure...no? Am I using the wrong pressure formula here?

Thank you in advance.

Get a scale and 3 pennies. Put 1 penny on the scale. What does the scale read? Put the second penny on top of the first penny. Now what does it read? Do the same with the third penny. Notice how the weight goes up each time? The idea is the same here.

Don't think about equations. Use common sense.