# Homework Help: Equations & Solutions

• yecko
In summary, the homework statement says that if you know the area, then the pressure is clear from the force of gravity on the weight divided by the area. The problem states that the top of the piston is "open to the air", which means that there is a pressure of the air acting on the piston.
yecko
Gold Member

## Homework Statement

http://i.imgur.com/wSvUEU2.png

## Homework Equations

(written in the photo)

## The Attempt at a Solution

(written in the photo)
Thanks

It all seems to be there, so I'm not sure what you are missing.

The area is clear from the 10cm cylinder. If you know the area then the pressure is clear from the force of gravity on the weight divided by the area (and + 1 atmosphere for the external pressure on the cylinder.) n is given, the Ts are given. What else do you need?

As Cutter Ketch noted, the pressure of the gas is not atmospheric pressure. The weight of the piston must be taken into account.

Do I really need to consider the weight of the piston? because it seems to be a constant factor... no change in the case...
Cutter Ketch said:
If you know the area then the pressure is clear from the force of gravity on the weight divided by the area (and + 1 atmosphere for the external pressure on the cylinder.)
do you mean "F=PA=mg" to be simple? however, what's going on with it?

Oh, I see. You aren't getting the right answer. So I take it the hand written answers are correct and the red is what you got?

Cutter Ketch said:
You aren't getting the right answer. So I take it the hand written answers are correct and the red is what you got?
Words in red are written by me
and the circle of the option is the right answer
i got c, while the right answer is a...
thanks

yecko said:
Do I really need to consider the weight of the piston? because it seems to be a constant factor... no change in the case...

do you mean "F=PA=mg" to be simple? however, what's going on with it?

You don't need it because it changes. You need it because you can't define the initial condition without it. Since h1 isn't given you have to figure it out. Your formula for h1 is correct, and in that formula is pressure. You need the absolute pressure to determine h1, and that pressure includes holding up the piston.

so you mean i should eliminate the factor for h1 first in order to find out the pressure if piston is not present?
how should i relate PV=nRT to force?

Your calculation in red is correct except for the value of the pressure P1. P1 does not equal atmospheric pressure.

To find the correct pressure, switch your attention to the piston and consider all the forces acting on the piston.

TSny said:
P1 does not equal atmospheric pressure
by F=PA=mg, P should be equal to mg/A=50*9.81/(0.05^2*pi)=62452Pa?
I still can't get the written answer...

yecko said:
by F=PA=mg, P should be equal to mg/A=50*9.81/(0.02^2*pi)=62452Pa?
That's not the pressure of the gas inside the container.

How many forces act on the piston? Describe each force.

TSny said:
Describe each force
weight and pressure by gas
am i right?

yecko said:
weight and pressure by gas
am i right?
There's one more force. The problem states that the top of the piston is "open to the air".

yecko
pressure of the air?
mg+P(a)A=P(g)A
P(g)=163689Pa ?

That's it. Good!

I'm off to bed. Will check back tomorrow.

Thanks you~
Then I will come back here at night of my local time~
because i am going to have exam tomorrow, hope all problems in the exercises can be settled by today:)

## What are equations and solutions?

Equations are mathematical expressions that use symbols and numbers to represent relationships between variables. Solutions are the values of the variables that make the equation true.

## Why is it important to understand equations and solutions?

Understanding equations and solutions is important because they are the basis for solving many real-world problems. It also helps develop critical thinking and problem-solving skills.

## What are the different types of equations?

There are several types of equations, including linear, quadratic, polynomial, exponential, and logarithmic equations. Each type has its own unique properties and methods for solving.

## How do I solve an equation?

To solve an equation, you need to isolate the variable on one side of the equation and perform the same operation on both sides to maintain balance. The solution is the value of the variable that satisfies the equation.

## What are some tips for solving equations?

Some tips for solving equations include writing down all the given information, simplifying both sides of the equation, using the correct operations, checking your answer, and practicing with different types of equations.

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