1 kg of iron and 1 kg of cotton are allowed to fall from the rooftop of a building simultaneously. Which one do you think will reach the ground first? Justify your answer.

Both the iron and the cotton, despite their different masses, will reach the ground at the same time if air resistance is ignored.
This is because, according to Galileo's principle of falling bodies, in the absence of air resistance, all objects fall with the same acceleration due to gravity. The acceleration due to gravity (gg) is approximately 9.8 m/s29.8 \, \text{m/s}^2 on Earth and is independent of the object's mass.
However, in reality, air resistance plays a role, especially for objects with larger surface areas or lighter masses. Cotton, being light and having a larger surface area compared to iron, will experience more air resistance. This resistance slows the fall of the cotton compared to the iron. Therefore, in real-world conditions where air resistance is present, the iron will likely reach the ground first because it has a smaller surface area relative to its mass and is less affected by air resistance.
Conclusion:
• In a vacuum (without air resistance): Both will hit the ground at the same time.
• In the presence of air resistance: The iron will reach the ground first due to less resistance acting on it compared to the cotton.