Newton’s First Law of Motion MCQs Quiz | Class 9
Take this Class IX Science (Code 086) quiz based on Unit III: Motion, Force and Work. This test specifically covers Newton’s First Law of Motion, including the statement of the law, the concept of inertia, mass relationship, and real-life examples like passengers in a moving bus. Answer the questions, submit to check your score, and download the solution PDF.
Overview: Newton’s First Law of Motion
Newton’s First Law of Motion, often called the Law of Inertia, states that an object remains in a state of rest or of uniform motion in a straight line unless compelled to change that state by an applied force. This law introduces the concept that objects have a natural tendency to resist changes in their state of motion.
Understanding Inertia
Inertia is the inherent property of a body that resists any change in its state of rest or motion. The mass of an object is a quantitative measure of its inertia. Heavier objects have more inertia than lighter ones.
- Inertia of Rest: An object at rest tends to stay at rest. Example: Dust comes out of a carpet when beaten; passengers fall backward when a bus starts suddenly.
- Inertia of Motion: An object in motion tends to stay in motion. Example: A passenger falls forward when a moving bus brakes suddenly.
- Inertia of Direction: An object tends to maintain its direction. Example: Mud flying off a rotating tire tangentially; being pushed sideways in a car turning a sharp corner.
Key Points to Remember
| Concept | Description | Real-life Example |
|---|---|---|
| Force Requirement | Unbalanced external force is needed to change velocity. | Kicking a football to start it moving. |
| Mass & Inertia | Directly proportional. More mass = More resistance. | Pushing a truck is harder than pushing a car. |
| Equilibrium | If net force is zero, velocity is constant (or zero). | A book lying on a table. |
Common Examples Explained
1. Shaking a tree branch: When you shake a branch vigorously, the branch moves, but the leaves/fruits tend to remain at rest due to inertia of rest and thus detach.
2. Luggage on a bus roof: Luggage is tied with a rope because if the bus stops suddenly, the luggage continues moving forward (inertia of motion) and may fall off.
Practice Questions
Try answering these to test your understanding further:
- Why does a bowler run before delivering a ball? (To build inertia of motion).
- Can a body have zero velocity but non-zero force acting on it? (Yes, e.g., at the instant of starting).
- Is force required to keep an object moving in deep space? (No, due to lack of friction).
- Which has more inertia: a cricket ball or a rubber ball of the same size? (Cricket ball, as it has more mass).
- Why do we tend to fall sideways when a vehicle turns? (Inertia of direction).
