When an object falls through the air, it experiences air resistance which increases with speed. Eventually, the object reaches a point where the air resistance equals the __________ and no longer accelerates.
Find the correct option-
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Gravitational force
A falling object is pulled down by its weight, the gravitational force, and held back by air resistance, which grows as the object speeds up. When the air resistance becomes equal to the gravitational force, the two forces balance and the net force on the object is zero.
With no net force there is no acceleration (Newton’s first law), so the object goes on falling at a constant speed, called its terminal velocity.
Why the other options are incorrect
Option (1) Frictional force — Incorrect. Air resistance is itself a frictional force (fluid friction); what it balances is the downward pull of gravity.
Option (2) Average velocity — Incorrect. It is a velocity, not a force, so it cannot be equal to air resistance.
Option (4) Centripetal force — Incorrect. It is the inward force that keeps a body moving in a circle; a body falling straight down needs none.