Here is the question I'm having trouble with: The average speed of a nitrogen molecule is about 6.70x10^2 m/s, and its mass is about 4.68x10^ -26 kg. (a) If it takes 4.20x10^ -13 s for a nitrogen molecule to hit a wall and rebound with the same speed but moving in an opposite direction (assumed to be the negative direction), what is the average acceleration of the molecule during this time interval? (b) What average force does the molecule exert on the wall? I've alread gotten the answer to part (a), I took the change in velocity over that interval of time ( -6.70x10^2 - 6.70x10^2) and devided it by the time. Which makes the answer to part (a) -3.19x10^15 m/s^2. I'm just lost on the second part. I must be using the wrong acceleration in the force equation or something. I know that F=ma but which acceleration do I use and maybe I didn't add all of the forces up? I don't know any help would be wonderful. Thanks in advance for your time.