Free Fall MCQs Quiz | Class 9
This quiz covers Class IX Science (Code 086), Unit III: Motion, Force and Work. The specific topic is Free Fall, focusing on the definition and conceptual motion under gravity. Test your understanding of how gravity affects objects in motion, submit your answers to see the score, and download the solution PDF for revision.
Understanding Free Fall and Motion Under Gravity
In physics, free fall is any motion of a body where gravity is the only force acting upon it. In the context of Class 9 Science, this concept explains why objects fall towards the Earth and how their velocity changes during the descent.
Key Concepts
- Definition of Free Fall: An object is said to be in free fall if it is dropped from a height and falls towards the earth under the influence of gravitational force alone. Air resistance is typically neglected in ideal calculations.
- Acceleration due to Gravity (g): The acceleration produced in freely falling bodies is the same for all bodies, irrespective of their mass. It is denoted by ‘g’. Near the surface of the Earth, its value is approximately 9.8 m/s/s.
- Direction of ‘g’: Gravity always acts downwards towards the center of the Earth. When an object is thrown upwards, ‘g’ acts against the motion (retardation), and when it falls down, ‘g’ acts in the direction of motion (acceleration).
Equations of Motion for Free Fall
The general equations of motion are modified for free fall by replacing acceleration ‘a’ with ‘g’ and distance ‘s’ with height ‘h’.
| Equation | Thrown Upwards (a = -g) | Falling Downwards (a = +g) |
|---|---|---|
| v = u + at | v = u – gt | v = u + gt |
| s = ut + 0.5at^2 | h = ut – 0.5gt^2 | h = ut + 0.5gt^2 |
| 2as = v^2 – u^2 | -2gh = v^2 – u^2 | 2gh = v^2 – u^2 |
Important Points to Remember
- The value of ‘g’ is not constant everywhere; it is greater at the poles and less at the equator due to the Earth’s shape (oblate spheroid).
- At the highest point of an object thrown upwards, the instantaneous velocity is zero, but acceleration is still ‘g’ acting downwards.
- If a feather and a coin are dropped simultaneously in a vacuum, they will hit the ground at the same time because ‘g’ does not depend on the mass of the object.
Extra Practice Questions
- Question: What is the value of ‘g’ at the center of the Earth?
Answer: Zero. - Question: If a ball is thrown up and takes 3 seconds to reach the top, how long does it take to come back down?
Answer: 3 seconds (Time of ascent = Time of descent). - Question: Does the acceleration due to gravity depend on the mass of the falling body?
Answer: No. - Question: What is the SI unit of weight?
Answer: Newton (N). - Question: How does ‘g’ change with altitude?
Answer: It decreases as we go higher above the Earth’s surface.
Content created and reviewed by the CBSE Quiz Editorial Team based on the latest NCERT textbooks and CBSE syllabus. Our goal is to help students practice concepts clearly, confidently, and exam-ready through well-structured MCQs and revision content.