# 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.

MY ANSWER:

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

Do I have the right idea?

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

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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