Paper II · Part B — Physics

Work, Power and Energy

Exam-focused notes, visual explanation, traps, revision sheet and every mapped past NDA question.

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Core5 mapped NDA questions

Build the idea

Build exam-ready understanding by connecting the core idea, formulas or facts, worked example and previous NDA questions. Focus on why each rule works, then test it under timed conditions.

Concept

Work is done when a force moves an object; power is the rate of doing work; energy is the capacity to do work. Mechanical energy is the sum of kinetic and potential energy.

Energy is conserved — it changes form but is neither created nor destroyed.

Key Points & Formulas

Work W = Force × displacement × cosθ (joule).
Power P = Work/time (watt); 1 horsepower ≈ 746 W.
Kinetic energy = ½mv²; potential energy = mgh.
Law of conservation of energy: total energy stays constant.

Worked Example

Q. A 2 kg ball is raised to a height of 5 m (g = 10 m/s²). Find its potential energy.

PE = mgh.

= 2 × 10 × 5 = 100 J.

Common traps

Reading the prompt too quickly and missing a qualifier.
Memorising the result without checking when it applies.
Skipping units, signs, chronology or the final reasonableness check.

NDA shortcuts

State the governing rule before substituting values.
Eliminate impossible options before doing full calculation.

One-screen revision sheet

Recall before you practise

Core definition
Most-used rule
One representative example

Past-paper bank

Practise every mapped question

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5 NDA questions

Choose an answer before the solution appears. Option order is mixed automatically.

Question 1

NDA I 2026

A constant power machine pulls a block on a smooth horizontal surface. Which one of the following correctly describes the relation between speed of the block ( $v$ ) and time ( $t$ )?

Question 2

NDA II 2025

The work done by the force acting on an object is zero if the displacement of the object

Question 3

NDA II 2024

A block of mass 2.0 kg slides on a rough horizontal plane surface. Let the speed of the block at a particular instant is 10 m/s. It comes to rest after travelling a distance of 20 m. Which one of the following could be the magnitude of the frictional force ?

Question 4

NDA II 2024

There is a ball of mass 320 g. It has 625 J potential energy when released freely from a height. The speed with which it will hit the ground is

Question 5

NDA I 2023

The power required to lift a mass of $8.0$ kg up a vertical distance of $4$ m in $2$ s is (taking acceleration due to gravity as $10$ m/s $^2$ ):

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