Class 10 Computer Science Chapter 1: Office Tools (Notes & Online Test) - PSEB

WORK, ENERGY AND POWER

Complete Study Notes & 5-Part Mega Quiz for NEET

1. Work Done by a Constant and Variable Force

In physics, work is said to be done when a force produces a displacement in the body. Mathematically, it is the dot (scalar) product of the force vector and the displacement vector.

$$W = \vec{F} \cdot \vec{d} = F d \cos\theta$$

• Positive Work: $\theta < 90^\circ$ (Force aids motion).
• Negative Work: $\theta > 90^\circ$ (Force opposes motion, e.g., Friction).
• Zero Work: $\theta = 90^\circ$ (Force is perpendicular to displacement, e.g., Centripetal force).

For a variable force, work is calculated by integrating the force over the displacement: $W = \int F(x) dx$, which is the area under the Force-Position graph.

2. Kinetic Energy & The Work-Energy Theorem

Kinetic Energy (K) is the energy possessed by a body due to its motion. $K = \frac{1}{2}mv^2$. It is related to momentum ($p$) by the equation $K = \frac{p^2}{2m}$.

The Work-Energy Theorem: The net work done by all the forces (conservative and non-conservative) acting on a body is exactly equal to the change in its kinetic energy.

$$W_{net} = K_f - K_i = \Delta K$$

3. Potential Energy & Conservation of Mechanical Energy

Potential Energy (U) is the stored energy of position. It is only defined for Conservative Forces (like gravity and spring force) where the work done is independent of the path taken.

• Gravitational Potential Energy: $U = mgh$
• Elastic Potential Energy of a Spring: $U = \frac{1}{2}kx^2$

Law of Conservation of Mechanical Energy: If only conservative forces do work on a system, the total mechanical energy (Kinetic + Potential) remains constant. $E_i = E_f$.

4. Power

Power is defined as the time rate at which work is done or energy is transferred.

$$P_{avg} = \frac{W}{t}$$
$$P_{inst} = \frac{dW}{dt} = \vec{F} \cdot \vec{v}$$

The SI unit of power is Watt (W). Commercial unit of electrical energy is kilowatt-hour (kWh), where $1 \text{ kWh} = 3.6 \times 10^6 \text{ J}$. 1 Horsepower (HP) = 746 W.

5. Collisions

A collision is an isolated event in which two or more colliding bodies exert relatively strong forces on each other for a relatively short time.

• Elastic Collision: Both momentum and kinetic energy are conserved. Coefficient of restitution $e = 1$.
• Inelastic Collision: Momentum is conserved, but kinetic energy is not. Some KE is lost as heat/sound. $0 < e < 1$.
• Perfectly Inelastic Collision: The bodies stick together after impact and move with a common velocity. Maximum KE is lost. $e = 0$.

← Back to NEET Resource Hub

🚀 NEET WORK & ENERGY MEGA QUIZ (100 MCQ)

Solve the 5 parts below to master Work, Energy, Power, and Collisions.

← Back to NEET Resource Hub