Final answer:
To determine the rock's acceleration when an astronaut exerts a force of 49.2 N, one must use Newton's second law of motion and divide the force by the mass of the rock, which is not provided in the question.
Step-by-step explanation:
If an astronaut exerts an upward force of 49.2 N on a rock, to find the rock's acceleration, we need to apply Newton's second law of motion. Newton's second law states that the acceleration (a) of an object is directly proportional to the net external force (F) acting on it and inversely proportional to its mass (m), following the formula a = F/m. However, the question provides only the force exerted by the astronaut and not the mass of the rock. If the mass of the rock were provided, we could simply divide the force by the mass to find the rock's acceleration.