1. The problem statement, all variables and given/known data I'm doing a lab and getting very confused. A cart is on a table. It is attached to a string which goes over a pulley. The pulley is on the edge of the table. On the end of the string there is a mass. When the mass falls straight down, it pulls on the string and makes the cart accelerate too. 2. Relevant equations Mass of the cart = 1 kg (constant) Trial 1: mass falling down: 0.1 kg & mass added to cart: 0.4 kg Trial 2: mass falling down: 0.2 kg & mass added to cart: 0.3 kg Trial 3: mass falling down: 0.3 kg & mass added to cart: 0.2 kg Trial 4: mass falling down: 0.4 kg & mass added to cart: 0.1 kg 3. The attempt at a solution I am supposed to graph the acceleration of the cart vs. the pulling force. However, I am not sure what this graph should look like. For trial 1, the pulling force would be (0.1 kg)*(9.81 m/s2)=0.981 N, right? And the theoretical acceleration would be 0.981 N/(0.4 kg+1kg) = 1.962 m/s2. However, if I graph a vs. F, I don't get a straight line, because the mass of the moving object is always changing. Is this right? In the book they make a big deal about the total mass of the system being constant, so I'm wondering if that has something to do with it.