Who among the following was the first to conclude that in vacuum all objects fall with the same acceleration g and reach the ground at the same time?

Galileo Galilei

The correct answer is option 3. Galileo Galilei.

Galileo Galilei, the renowned Italian physicist, mathematician, and astronomer, was the first to conclude that in vacuum (or in the absence of air resistance), all objects fall with the same acceleration and reach the ground at the same time, regardless of their mass. This groundbreaking insight was a departure from the prevailing Aristotelian view that heavier objects fell faster than lighter ones.

Galileo's conclusion came from his famous thought experiment involving the Leaning Tower of Pisa. While he likely didn't actually conduct this experiment, the concept behind it illustrates his understanding of gravity. Galileo reasoned that if two objects, one heavier than the other, were dropped from the same height simultaneously, they would hit the ground at the same time. This conclusion challenged the Aristotelian belief system and laid the groundwork for modern physics.

Galileo's understanding of free fall and the uniform acceleration of gravity laid the foundation for Isaac Newton's laws of motion and universal gravitation, which would revolutionize our understanding of the physical world.