1. The problem statement, all variables and given/known data Suppose an oxygen molecule traveling at the speed of 484 m/s bounces back and forth between opposite sides of a cubical vessel 0.1 m on a side. What is the average force the molecule exerts on one of the walls of the container? 2. Relevant equations F=p/t 3. The attempt at a solution t=0.2 m / 484 m/s = 4.13 *10^-4 seconds In a collision v changes direction so delta p = 2*mv (mv was calculated in a previous question so it is known) The average force can then be calculated as: F = 2mv / t My question here is, how come when calculation the time, they use 0.2 m and not 0.1 as given in the assignment? Is this because the molecule moves back and forth 0.1 m during the collision? Second question: why do they multiply a factor 2 on the impulse? Where does this come from?