Final answer:
Doubling the net force on an object while keeping its mass constant leads to a doubling of the acceleration; hence, from 6.0 m/s², the new acceleration would be 12.0 m/s².
Step-by-step explanation:
If an object has an acceleration of 6.0 m/s² and the net force acting upon it is doubled, the new acceleration would be calculated using Newton's second law of motion, which states that the force acting on an object is equal to the mass of the object multiplied by the acceleration of the object (F=ma).
In this case, since only the force is doubled and the mass remains constant, the acceleration is also doubled. Therefore, the new acceleration of the object would be 12.0 m/s².