In a student experiment, a constant-volume gas thermometer is calibrated in dry ice (−78.5°C) and in boiling pentane (36.1°C). The separate pressures are 0.890 atm and 1.423 atm. Hint: Use the linear relationship P = A + BT, where A and B are constants.

(a) What value of absolute zero does the calibration yield?


(b) What pressure would be found at the freezing point of water?

(c) What pressure would be found at the boiling point of water?


i dont know how to solve for 2 variables wtf? lol.... forgot or im looking at it wrong... please help.

first step is to
"From the linear relationship, we know that the pressure is related to the temperature as P = A + BTc, where A and B are constants, and Tc is the Celsius temperature. To find A and B, we use the given data ".

so its setup like 0.890 atm = A + (-78.5) B

and

1.423 atm = A + (36.1) B


so you need to solve for a and b? no clue how and then after?

thanks





also one other question:
"What is the percentage increase in the moment of inertia of the object when it is warmed from 17°C to 100°C if it is composed of steel? Assume the average linear expansion coefficients shown in the Table of Average Coefficients of Expansion do not vary between 17°C and 100°C. "

i got 0.22 % but its wrong?



using this table.

This post was edited by noob_whacker on Nov 2 2015 11:44am

It's just an algebra two problem. Rearrange the first equation A = .89 + 78.5B

Plug A into the second equation and solve for B. Now plug B into the first and solve for A.

You get something like A = 1.25..... And B = .004....

I assume at absolute zero they want you to just plug 0 into P and solve for T.

For part 2 and part three just put 0 and 100 in for T and solve for P.

Question 2:

This depends on "Object", but I'm just going to assume a cylinder and use the following equation.

I = .5MR^2

dI/dt = MRdR/dt

Thermal expansion equation: R(t) = R(1+ At)
dr/dt = RA

dI/dt = MR^2A = 2IA

dI = 2IAdt

Comes out to something like .18....

This post was edited by RzChaos on Nov 2 2015 04:35pm

ok thanks but the percent should be the same per object?

Consider an object with any one of the shapes displayed in the table below.
it has 6 objects , hoop or thin cylindrical shell, solid cylinder or disk, solid sphere, thin spherical shell, long ting rod with rotation axis through end, and long thin rod with rotation axis through center.

part a was what i posted in first post about the steel. but part b is
What is the percentage increase in the moment of inertia of the object when it is warmed from 17°C to 100°C if it is composed of lead? Assume the average linear expansion coefficients shown in the Table of Average Coefficients of Expansion do not vary between 17°C and 100°C.

and the answer i got correct was 0.48%

then part c asks, " (c) Why are the answers for parts (a) and (b) the same for all the shapes?" so i guess shape should not matter? how do u answer c?

thanks again!




also how do u do this one if you dont mind? thanks, lost on it

The surface area of an unclothed person is 1.75 m2, and his skin temperature is 33.0°C. The person is located in a dark room with a temperature of 11.0°C, and the emissivity of the skin is e = 0.95. (Include the sign of the value in your answer.)

(a) At what rate is energy radiated by the body?

(b) What is the significance of the sign of your answer?

bump, plz help

Stefan Boltzman Law, very simple problem, plug and chugg. Make sure you have the right units on everything. That includes converting Celsius to Kelvin BEFORE you take temperatures to the fourth power.

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/stefan.html

Since Tc < T, you will get a positive answer meaning that the skin is radiating heat, not absorbing it.

This post was edited by Dontrunaway on Nov 3 2015 07:19pm

For your MOI problem...

If you notice in the following picture, all of the moments of inertia vary based on the square of the "length" dimension (radius, or rod length), which is what you are assuming is going to change linearly with temperature change etc.

The change for every shape will be the same percentage wise because every single one has the same term "Length^2" and you are only changing length.

hmmmm thanks for the help guys!

but i still dont understand the first question

In a student experiment, a constant-volume gas thermometer is calibrated in dry ice (−78.5°C) and in boiling pentane (36.1°C). The separate pressures are 0.890 atm and 1.423 atm. Hint: Use the linear relationship P = A + BT, where A and B are constants.

(a) What value of absolute zero does the calibration yield?


(b) What pressure would be found at the freezing point of water?

(c) What pressure would be found at the boiling point of water

This post was edited by noob_whacker on Nov 16 2015 02:14pm

bump plz help


im so close to answer, but stuck

This post was edited by noob_whacker on Nov 17 2015 04:56pm

Not sure what you are confused about. Substitute the values you are given into the equation:

(1) .89 = A + B (-78.5C)
(2) 1.423 = A + B (36.1C)

(1) A = .89 - B (-78.5C)

(2) 1.423 = .89 - B(-78.5C) + B(36.1C)

Solve this for B. Put this value of B into (1) and solve for A.

You now have an equation: P = A + BT, where you know both A and B

For part 1, put P = 0 and solve for T
For part 2, put T = 0C and solve for P
For part 3, put T = 100C and solve for P


This post was edited by RzChaos on Nov 17 2015 05:30pm

cant solve for b....


been forever since i took algebra

so i get 1.423 + B (-78.5) - B (36.1) =.89
then B (-78.5) - B (36.1) = -0.533
then B - B (36.1) = 0.006789809
then B - B = 0.000188083

B cancel?

obviously im doing something wrong, prob simple but i dont know

im lost.

This post was edited by noob_whacker on Nov 18 2015 02:55pm