This is a suggested answer to the GCE O Level Pure Physics examination, year 2019, Paper 1, multiple choice question 6.
The question stated that a heavy object was dropped from the aeroplane and its velocity measured at two points before it hits the ground were found to be the same.
The student is required to pick the right explanation for this.
The answer is C. That is, the force on the object due to air resistance is equal to the object’s weight.
When an object falls, the earth’s gravitational pull on the object exerts a downward force which is the weight of the object. This downward force causes an acceleration. However, in the presence of air atmosphere, there is air resistance, which is a frictional force that opposes the downward motion. The air resistance will increase with the increasing velocity of the falling object. A point will reach where the air resistance equals the weight of the object. At this point, the object no longer accelerate and continue to fall at terminal velocity which is a constant velocity.