Law of Conservation of Energy MCQs Quiz | Class 9
Test your understanding of the Law of Conservation of Energy for Class IX Science (Code 086), Unit III: Motion, Force and Work. This quiz covers the statement of the law and various energy transformations (excluding commercial units). Answer the questions below, submit your response to see your score, and download the detailed PDF solution.
Understanding the Law of Conservation of Energy
The Law of Conservation of Energy is a fundamental principle in physics. It states that energy can neither be created nor destroyed; it can only be transformed from one form to another. The total energy of an isolated system remains constant (conserved) over time.
Key Concepts
- Statement: In any closed system, the total amount of energy remains the same, though it may change forms (e.g., from potential to kinetic).
- Mechanical Energy: The sum of kinetic energy (KE) and potential energy (PE) of an object is its total mechanical energy. For a freely falling body, as height decreases, PE decreases and KE increases, but $PE + KE = \text{constant}$.
- Pendulum Example: In a simple pendulum, energy oscillates between potential energy (at extreme points) and kinetic energy (at the mean position).
Common Energy Transformations
| Device / Process | Transformation |
|---|---|
| Electric Bulb | Electrical Energy -> Light + Heat Energy |
| Falling Stone | Potential Energy -> Kinetic Energy |
| Microphone | Sound Energy -> Electrical Energy |
| Photosynthesis | Light Energy -> Chemical Energy |
Quick Revision Points
- At the highest point of a throw, Kinetic Energy is zero, and Potential Energy is maximum.
- Just before hitting the ground, Potential Energy is zero (relative to ground), and Kinetic Energy is maximum.
- Friction often converts mechanical energy into heat energy, but the total energy of the universe is still conserved.
Extra Practice Questions
- What happens to the total energy of a body falling freely towards the earth? (Ans: Remains constant)
- Name the energy transformation in a dry cell battery. (Ans: Chemical to Electrical)
- When you stretch a rubber band, what energy is stored? (Ans: Elastic Potential Energy)
- Is it possible to create energy in a laboratory? (Ans: No, only transformation is possible)
- During the oscillation of a pendulum, at which position is the kinetic energy maximum? (Ans: Mean position)
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