Final answer:
The tension in the connecting string between two blocks of different mass, accelerated by a force, will be less than the force pulling the leading block due to the need to accelerate both blocks.
Step-by-step explanation:
When two blocks of different mass are connected by a string and pulled by a force, the tension tension in the string will be less than the force pulling the leading block if there is acceleration involved. This is because the string must accelerate both blocks, not just one. In the ideal case where the system only experiences the force from the rubber band and there are no other forces like friction or air resistance acting on the system, the tension in the string indeed accelerates both masses. Using Newton's second law, F = ma, for a system of interconnected blocks, it is clear that the total force exerted by the rubber band is divided between not only accelerating the less massive block but also overcoming the inertia of the more massive block connected by the string.
Therefore, if we consider the rubber band to apply a force F on the less massive block while both blocks are accelerating, the tension in the string T will have to be less than the applied force F. The tension must be sufficient to accelerate the more massive block, while the remaining force from the rubber band is used to accelerate the less massive block. This corresponds to multiple forces and their reactions within the system as per Newton's third law. If there was no acceleration, and if the blocks moved at constant velocity, the tension in the string would be equal to the force applied by the rubber band.