The number density of atoms (mostly hydrogen) in interstellar space is about 10 per cm3, and the temperature is about 100K. a. Calculate the pressure of the gas in interstellar space, and express it in atmospheres. b. Under these conditions, an atom of hydrogen collides once every 109 s. By using the root-mean-square speed, estimate the distance traveled by a hydrogen atom between collisions. Compare this distance with the earth-sun distance of 1.5x108 km.