# Doubt from thermodynamics

This a very basic question..but I am getting different answer when I apply work energy theorem and force method to solve for final pressure..the method by force yields correct answer ...someone pls vedify. ..

800 K, for the first one?

Bro that is correct..did you solve by work method?

Not force waala method bro..facing problem when using work energy theorem..
I am getting final pressure to be different in the 2nd method...

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ok bro i will try in work energy method also, i get i will post it @pushkar_2020

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20 too..with explanation

bro i am getting 10^(-5/3) cm , which are not in options..

What method did you take? ?

Let intermolecular distance be D then in a volume $\frac{4 \pi}{3} D ^3$ there is only one

$\frac{4 \pi}{3} D ^3P = \frac{1}{N_A }= R_T \: \: \: or \: \: D = \left ( \frac{3RT}{4\pi N_AP} \right )^{1/3}$

I too got something..

or, we can use
P = (n/v)KT
N=P/KT
then we will get volume occupied by 1 molecule
then side length = (volume)^1/3

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This is not giving the same answer. .