In all these questions, once you have determined the acceleration for the group, then the tension (or force in between if it is pushing it) will necessarily be the acceleration times all the mass that is being pulled (or pushed as the case may be.)thanks a lot, that helped me tremendously. :)
i get it now, but there is another part where it says that another duck(1 kg) is added, and it is put at the front of the row.
DUCK2(2kg)------DUCK1(5kg)------DUCK3(1kg)----->(10N)
Now it asks for the tension connecting ducks 2(2kg) and 3(1kg)and then the tension of ducks 1(5kg) and ducks 2(2kg) . would the tension still be equal to the inertial force of the last duck(2kg)? or would it now be equal to the inertial force of the middle duck(5kg)?