# Exam review question on thermodynamics [closed]

A cube has a side length of $20\text{ cm}$. An atom in the gas moves around the cube as shown. It continually bounces off the four lateral walls of the cube. The atom has a mass of $6.6\times 10^{-27}\text{ kg}$. Because of the elastic collisions with the walls, the atom maintains its speed of $300\text{ m/s}$ as it moves around. The figure below shows the view from above looking down into the cube at the path of the atom.

The repeated hits cause there to be a force applied to each of the four lateral faces. Find the force (in Newtons) that it applies to Face 1. Find the force it applies to Face 2.

$$2 \sin(\theta)m v = 2 \sin(60) (6.6\times 10^{-27}) 300\text{ m/s} = 1.2 \times 10^{-24}$$

Do I have the right idea?

-

## closed as too localized by David Z♦Feb 3 '12 at 2:46

This question is unlikely to help any future visitors; it is only relevant to a small geographic area, a specific moment in time, or an extraordinarily narrow situation that is not generally applicable to the worldwide audience of the internet. For help making this question more broadly applicable, visit the help center. If this question can be reworded to fit the rules in the help center, please edit the question.

I get the feeling these types of questions are not welcome on this forum and I am wondering if there is a better forum to ask questions similar to this? –  rudolph9 Feb 3 '12 at 2:06
Hi Kurt! Actually this isn't a forum, it's a Q&A site. The point is to collect questions that are useful to everyone, not just to the person asking them. This type of question, where you just show a calculation and ask "Am I doing this right?", is only useful to you. If you can rewrite the question to ask about the specific physical principle that you're confused about (for example: "I don't understand why <formula> gives the force on the wall"), then it might be a better question for this site. I'll be happy to advise you on how to improve this question if you want to do so. –  David Z Feb 3 '12 at 2:46
(cont.) If you would rather not put in the effort to improve the question, you could take it to Physics Forums. –  David Z Feb 3 '12 at 2:47