Answer:
Object 4 in the example
Explanation:
For simplicity and a clearer view of this problem, let's assume that four masses from 1 to 4 have the the masses 2 kg, 4 kg, 6 kg, 8 kg respectively.
According to the second Newton's law, we know that force is directly proportional to both mass and acceleration. The equation representing this is .
Notice that all of them have the same acceleration. This means, the greater the mass, the greater the force for a fixed acceleration. Simply speaking, the forces for each of the objects would be 2a, 4a, 6a and 8a respectively.
Since we're interested in the magnitude of the force and not direction, we neglect whether acceleration is positive or negative. This means that object 4 will require the greatest force to move, as it has the greatest mass.