1. The problem statement, all variables and given/known data I am stuck on this problem: So the question is asking for F21, F12, F32, and F23. (That's the force by 2 on 1). The mass of m2 is variable. There are four cases where I need to solve for the forces: when m2 has mass of 3kg, 0.3kg, 0.03kg, and 0kg. The mass of m1 = 2.5kg, the mass of 3 = 3.5kg. Also assume that friction is neglected. I am confused on how to resolved the tension force in a system with numerous objects. The T is constant, 3N. imagine there's a person pulling on the string with a constant force of 3N. I know the acceleration of all three carts in each case should be the same. But how do I solve for the tension force in the strings between the carts? 2. Relevant equations F=ma Newton's 3rd Law Pretty sure that's all I really need here. 3. The attempt at a solution Ok, so I drew free-body-diagrams for each case. I know T is always equal to 3N. The weight force and normal force of all three carts aren't taken into account. Should the tension force in the strings be constant? Suppose I were to do case 1 with m2 = 3kg: T=3N Fnet = 3N 3 = (m1+m2+m3)a a = 3/(2.5+3+3.5) = 0.33 m/s/s (for the whole system, so each cart has the same acceleration) Going from left to right, solving for F23, would the force m2 on m3 be equal to (m2+m1)0.33? Then would F32 be equal in magnitude but in the opposite direction of F23 because of Newton's 3rd Law? I'm not sure what to include or exclude when I'm calculating a force within a specific part of a system. Any pointers would be very helpful. Thanks.