sorry i got one more question, its conceptual and i have a little problem with it, 1. The problem: Bill and Susan are both standing on identical skateboards (with really good ball bearings) initally at rest. Bill weighs three times as much as susan. Bill pushes horizontally on Susan's back, causing susan to start moving away from Bill. Immediately after Bill stops moving. We are give many choices and asked to pick the correct statement, the two that i have a problem with are: a) Susan is is moving away from Bill, and Bill is stationary b) Susan and bill are moving away from each other, and susan's speed is three times larger than that of Bill. 2. Relevant equations Ok i think Newton's thrid law applies here and Fnet=ma 3. The attempt at a solution The correct answer is (b) however i have a problem with that, ok i know that the force Bill is exerting on susan is equal and opposite to the force susan is exerting on Bill however it is possible that susan starts moving while bill is stationary because the static friction of bill is larger than that of susan because his weight is more and therefore his normal force is larger. however i dont think its correct to say that if they both overcame their static friction that susan's SPEED would be three times larger shouldnt it be her ACCELERATION that is three times larger not her speed? because of Fnet=ma?