Question

Among which of the following situations the object(s) is/are in free fall?

1. An object dropped from a certain height.
2. An object is thrown upward or a person jumping off the ground.
3. Flying in a aircraft.
4. A car accelerating at $9.8m{s}^{-2}$in the road.

• A. Only 1^st is in free fall.
• B. Only 3^rd is in free fall.
• C. Only 1^st and 2^nd are in free fall.
• D. Only 1^st and 3^rd are in free fall.

Answer 1

The correct option is C

Only 1^st and 2^nd are in free fall.

Free fall is any motion of a body where gravity is the only force acting upon it.
In 1^st activity, an object is moving downwards, due to gravitational force of attraction. There is no other force acting on it except the gravitational force.
Similarly, in 2^nd activity, the object is in free fall even when moving upwards or instantaneously at rest at the top of its motion.
Here, for both the above cases, we have assumed that the air resistance is negligible as compared to the weight of the object.
In 3^rd and 4^th activity, since gravity is not the only force acting on the aircraft and car, it is not a free fall.