Question

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.

Answer 1

Hint: The gravitational acceleration that acts on an object only depends on the gravity of the earth and not the kind of object. Hence it acts equally on iron and cotton. However, air resistance will act differently on both the objects depending on their shape and density.

Complete step by step answer:
When an object is dropped from a height, the Earth’s gravitational acceleration pulls it downwards towards the surface. The acceleration of the object will be equal to the gravitational acceleration of the Earth’s gravity.
Theoretically, both the objects irrespective of their masses should experience the same acceleration and hence they should both reach the ground at the same time. In reality, however, there is resistance in the form of air drag that is experienced by the objects. This friction force depends on both the shape of the object and its density.
Now cotton is highly porous and experiences a much higher air resistance than iron. As a result, it will fall much slower to the ground and in the process also get displaced from its original path. So, the piece of iron will reach the ground first.

Note: The mass of the objects given to us in the question is to mislead us since the gravitational force acting on both the objects will be equal irrespective of their masses. This has been proven in big rooms where a vacuum was created and a light object such as a feather and a heavy object such as a bowling ball dropped to the ground at the same speed since there was no air resistance in the room.