Class IX :: Chapter 11 - WORK AND ENERGY
Chapter-wise Multiple Choice Questions with Instant Feedback
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- Scientific Work: Work is done only when a force causes displacement in its direction. W = F × s (in joules).
- Zero Work: No work is done if force is perpendicular to displacement or if there is no displacement.
- Energy: Capacity to do work. SI unit: joule (J).
- Kinetic Energy (KE): Energy due to motion. KE = ½ m v².
- Potential Energy (PE): Energy due to position or shape. Gravitational PE = m g h.
- Law of Conservation of Energy: Energy can neither be created nor destroyed; it only changes form.
- Mechanical Energy: Sum of KE and PE. Remains constant in an isolated system.
- Power: Rate of doing work. P = W/t. SI unit: watt (W).
- Commercial Unit of Energy: Kilowatt-hour (kWh). 1 kWh = 3.6 × 10⁶ J.
- Work-Energy Theorem: Work done on an object equals the change in its kinetic energy.
- Positive & Negative Work: Positive if force and displacement are in same direction; negative if opposite.
- Efficiency: Ratio of useful energy output to total energy input, often expressed as percentage.
Basic Level Questions
Chapter Summary
Work and Energy introduces the fundamental concepts that explain how forces cause changes in motion and how energy is transferred and transformed in physical systems. You'll move beyond everyday notions of “work” to understand its precise scientific definition—where work is done only when a force produces displacement. The chapter seamlessly connects work to energy, exploring its various forms like kinetic and potential energy, and establishes the powerful Law of Conservation of Energy, a cornerstone principle in physics.
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