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## Homework Statement

In outer space, the density of matter is about one atom per cm^3, mainly hydrogen atoms, and the temperature is about 3.4K. Calculate the average speed of the hydrogen atoms, and the pressure (in atmospheres)

M_H = 1.0079au = 1.67 X 10^-27 Kg

1 Hydrogen atom per cm^3 = 100 hydrogen atoms per m^3

K (Boltzmann's constant) = 1.381 X 10^-23

T = 3.4K

## Homework Equations

m[tex]\bar{}v[/tex]^2 /2 = 3kT/2

PV = Nm[tex]\bar{}v[/tex]^2 /3

## The Attempt at a Solution

part 1:

m[tex]\bar{}v[/tex]^2 /2 = 3kT/2

[tex]\bar{}v[/tex] = [tex]\sqrt{}3(1.381 X 10^-23)(3.4)/(1.67 X 10^-27)[/tex]

[tex]\bar{}v[/tex] [tex]\approx[/tex] 300m/s

part 2:

Consider V = 1m^3

PV = Nm[tex]\bar{}v[/tex]^2 /3

P =Nm[tex]\bar{}v[/tex]^2 /3V

=(100)(1.67 X 10^-25)(300)^2/3(1)

P [tex]\approx[/tex] 5X 10^-19 N/m^2 [tex]\approx[/tex] 5 X10^-24 atm

As usual, I get the first part of the question right, but the answer to the second part is 5 X 10^-22 not ^-24. Anyone know what I'm doing wrong?