Consider an ideal gas composed of helium atoms. The collisions between atoms are similar...

Consider an ideal gas composed of helium atoms. The collisions between atoms are similar to the collisions between billiard balls. That is, whenever the distance between two atoms is less than 2r (where r is the radius of a helium atom), the two atoms undergo a collision. Show that the mean free path between collisions , is proportional to is the density of the gas. Hint: Consider the motion of just one atom and assume the others are all “frozen” in place.