Final answer:
The force that the 4.0 kg block exerts on the 3.0 kg block should be equal to the weight of the 4.0 kg block if only gravity is considered, which is 39.2 N. Without additional context, the correct answer cannot be determined from the given options.
Step-by-step explanation:
The force exerted by the 4.0 kg block on the 3.0 kg block can be found using Newton's third law of motion, which states that every action has an equal and opposite reaction. If it is assumed that the 4.0 kg block is exerting a force on the 3.0 kg block due to gravity, and both blocks are on a horizontal surface where there is no acceleration, the force must simply be the weight of the 4.0 kg block.
The weight is calculated as the mass of the block (4.0 kg) multiplied by the acceleration due to gravity (9.8 m/s2), which equals 39.2 N. However, this doesn't align with the given options, suggesting that there might be additional context that is necessary to properly answer this question. Without that context, the correct answer cannot be definitively provided. Extra consideration should be given to forces such as friction or any applied forces that may change the net force exerted by the 4.0 kg block on the 3.0 kg block.