[SOLVED] Motion (newton's 2nd law + weight question) 1. The problem statement, all variables and given/known data A waterskier of mass 70 kg is towed in a northerly direction by a speedboat with a mass of 350 kg. The frictional forces opposing the forward motion of the waterskier total 240 N. (a) If the waterskier has an acceleration of 2.0 m due north, what is the tension in the rope towing the waterskier? (b) If the frictional forces opposing the forward motion of the speedboat total 600 N, what is the thrust force applied to the boat due to the action of the motor? 2. The attempt at a solution I answered a) correctly getting the tension as 380N north. For part b) though I got the answer wrong. According to the solutions it says that the mass used in for Fnet = ma is 350kg. Why? Doesn't the boat also pull the skier? So the net weight it 420kg? I'm confused as to why they used 350kg rather than 420kg. Same with part a), although I got it correct, looking back I'm not sure why 70kg is used rather than the combined mass of 420kg. So, in problems with two objects connected by a string, why is the mass of an object ONLY it's mass rather than the added mass of both, because isn't the mass pulled by the object the overall mass of the pair? Sorry if I'm not clear :( Thanks!