All questions of Work, Energy and Power for UPSC CSE Exam

Understanding Work in Physics
Work is a fundamental concept in physics that describes the transfer of energy when a force is applied to an object over a distance.
Correct Expression for Work
The correct expression for work is given by:
- W = F * ds
Where:
- W is the work done,
- F is the force applied,
- ds is the displacement in the direction of the force.
Why Option A is Correct
- Force and Displacement: Work is defined only when a force causes displacement. If there is no movement, no work is done regardless of the amount of force applied.
- Direction Matters: The displacement must be in the direction of the force. If the force and displacement are at an angle, only the component of the force in the direction of the displacement does work.
Other Options Explained
- W = P/t: This equation relates power (P) to work done over time (t), but it is not the direct definition of work.
- W = E: This suggests work equals energy, which is misleading. Work results in a change in energy, but they are not equivalent in definition.
- W = E/t: This equation describes power as work done over time, but again, it does not represent the definition of work.
Conclusion
In summary, option A (W = F * ds) correctly encapsulates the essence of work in physics, emphasizing the relationship between force, displacement, and the direction of motion. Understanding this principle is crucial for physics applications, including those relevant to the Delhi Police Constable category.

Understanding Energy
Energy is a fundamental concept in physics that relates to the capacity to do work. It plays a crucial role in various fields, including engineering, physics, and environmental science.
Definition of Energy
- Energy can be defined as the ability to create work.
- This definition emphasizes that energy is not just about performing work but also about being capable of doing it.
Clarifying Other Options
- Option a: Work - While work is a form of energy transfer, it is not energy itself. Work is done when energy is transferred from one system to another.
- Option c: Quantification of Work - Energy is indeed measured in terms of work, but describing energy as merely a quantification misses its broader definition as a capacity.
- Option d: Force multiplied by Displacement - This describes how work is calculated, not energy itself. Although work involves energy transfer, it does not define energy.
Types of Energy
- Kinetic Energy - Energy associated with moving objects.
- Potential Energy - Energy stored in an object due to its position or configuration.
- Thermal Energy - Energy related to the temperature of an object.
Conclusion
In summary, energy is fundamentally the ability to do work. Understanding this concept is vital as it connects various physical phenomena and aids in comprehending how systems interact in terms of energy transfer and conversion.

Introduction to Joule
The unit of energy, known as the Joule (symbol: J), is named after the renowned English physicist James Prescott Joule. His significant contributions to the field of thermodynamics and energy have established him as a pivotal figure in physics.
James Prescott Joule's Contributions
- Born in 1818: Joule was born in Salford, England, and had a keen interest in science from a young age.
- Key Experiments: Joule conducted several groundbreaking experiments that demonstrated the relationship between mechanical work and heat. He is best known for his work on the conservation of energy, which ultimately led to the formulation of the first law of thermodynamics.
- Mechanical Equivalent of Heat: One of his most famous experiments involved determining the mechanical equivalent of heat. He discovered that the amount of work done on a system is equivalent to the heat produced, establishing a foundational principle in thermodynamics.
Legacy and Impact
- Recognition in Physics: The Joule is a standard unit in both the International System of Units (SI) and the field of physics, widely used to measure energy, work, and heat.
- Honor in Naming: By naming the unit after him, the scientific community honors Joule's dedication to understanding energy and its transformations, which has paved the way for advancements in various branches of science and engineering.
Conclusion
In summary, the correct answer is option 'A', as James Prescott Joule's pioneering work laid the groundwork for modern physics and the understanding of energy, making his name synonymous with the unit of energy itself.