1. The problem statement, all variables and given/known data Two bodies are standing still upon a surface without friction. The mass of body 1 is bigger than the mass of body 2. i) A constant force is applied to body 1, so it accelerates in a segment to a distance d. The force stops being applied to body 1, and is applied to body 2. When body 2 has done the distance d, which of the following are valid? ii) When a force is applied to body 1, it accelerates for a time Δt. The force stops being applied to body 1, and is then applied to body 2. Which are valid if body 2 accelerates for Δt? a) p1 < p2 b) p1 = p2 c) p1 > p2 d) K1 < K2 e) K1 = K2 f) K1 > K2 2. Relevant equations I = ΣFΔt Δpf = Δpi 3. The attempt at a solution I think I'm done with (ii), but here's a look: ii) I = FΔt => I1 = I2 => Δp1 = Δp2 => pf1 - pi1 = pf2 -pi2 => pf1 = pf2 (1) m1 > m2 (2) (1) & (2): V1 < V2 (3) K = 1/2*m*V2 (4) (2) & (3) & (4): K1 < K2 The book has b & d as the answers for (ii), and c & e as the answers for (i). Now, it's one (i) I have a problem with. I just don't know how to tackle it. ΔP = 0 is for whole isolated systems, and for a very small time-frame. Here, from what I gather, I hit 1, it accelerates, it reaches d, and then the force stops being applied to it (so technically it keeps going on and on since there's no friction). After that, I do the same to 2. I'm probably missing something (I just got into the chapter, I'm five pages in so I haven't really gotten the hang of it yet), so I'd be grateful for any help!