Short Answer 
The analysis of a system with three identical blocks connected by strings on a frictionless surface begins by recognizing the applied force of 4.5 N and the mass of each block as 0.400 kg. Calculating the acceleration yields 3.75 m/s², and summing the total mass of all blocks leads to a confirmation of the total force as 4.5 N.
Step 1: Understand the System
To analyze the system of three identical blocks connected by ideal strings, we recognize that they are being pulled along a horizontal, frictionless surface with a force F of 4.5 N. Each block has a mass of 0.400 kg. It’s crucial to ascertain how these components interact through the tension in the strings and how that affects their motion.
Step 2: Calculate Acceleration
Since the force is applied to the entire system, all blocks experience the same acceleration due to the tension created by the connected strings. Using the formula F = (m_A + m_B) * a, we can solve for acceleration (a). Given that the combined mass of blocks A and B is 0.800 kg, we find a = 3.75 m/s².
Step 3: Determine the Total Force
Next, to find the magnitude of the force acting on the entire system, we use the formula F = (m_A + m_B + m_C) * a. Adding up the masses of all three blocks gives us 1.2 kg. Multiplying this combined mass by the previously calculated acceleration results in a total force of 4.5 N, confirming our understanding of the forces within the system.