Chapter 10: Work and Energy | Summary

Energy is defined as the capacity to do work. The SI unit of energy is also joule (J). It is a scalar quantity.

Energy exists in many forms: kinetic energy, potential energy, heat energy, chemical energy, electrical energy, and light energy.

Energy can be stored and transferred, and one form of energy can be converted into another.

Kinetic energy is the energy possessed by an object due to its motion. It is directly proportional to the mass and the square of the velocity of the object.

The formula for kinetic energy is: KE = ½ mv², where m is mass and v is velocity.

Faster-moving or heavier objects have greater kinetic energy, such as a moving car, bullet, or wind.

Potential energy is the energy possessed by an object due to its position or configuration.

For gravitational potential energy, it is defined as the work done in raising an object against gravity to a certain height.

The formula is: PE = mgh, where m is mass, g is acceleration due to gravity, and h is height.

The law states that energy can neither be created nor destroyed; it can only be transformed from one form to another.

The total energy in a system remains constant even though it may change from kinetic to potential or vice versa.

For example, during the free fall of an object, potential energy is continuously converted to kinetic energy, but the total mechanical energy remains the same.

Power is the rate at which work is done or energy is transferred. It is measured in watts (W).

Power = Work / Time. 1 watt = 1 joule per second (1 W = 1 J/s). Larger units include kilowatt (1 kW = 1000 W).

Average power is calculated by dividing the total energy consumed by the total time taken.

In households, energy is measured in kilowatt-hours (kWh), where 1 kWh = 3.6 × 10⁶ J.

Electric bills are calculated using this unit, with typical devices rated in watts or kilowatts.

Energy consumption depends on the power rating and duration of usage.

Work – Product of force and displacement (W = F × d).

Energy – Capacity to do work; measured in joules.

Kinetic Energy – Energy due to motion (KE = ½ mv²).

Potential Energy – Energy due to position (PE = mgh).

Power – Rate of doing work (P = W/t), unit: watt.

Commercial Unit of Energy – Kilowatt-hour (kWh).

Positive Work – Force and displacement in same direction.

Negative Work – Force opposite to displacement.

Mechanical Energy – Sum of kinetic and potential energy.

Law of Conservation of Energy – Total energy remains constant.