Final answer:
The investigation could be based on the hypothesis that the acceleration of a toy car is directly proportional to the force applied, as per Newton's second law of motion.
Step-by-step explanation:
A possible hypothesis for this investigation might be that the acceleration of an object is directly proportional to the force applied to it, assuming that the mass of the object remains constant. This is based on Newton's second law of motion, which states that acceleration is produced when a force acts on a mass, and the greater the force, the greater the acceleration provided that the mass is constant. Therefore, when the student pushes the toy car with more force, the car should exhibit a greater acceleration.