Work, energy and power — KCSE Physics

KCSE Physics · 108 practice questions · 7 syllabus objectives

37 easy38 medium33 hard

What You'll Learn

Key learning outcomes for this topic, aligned to the KNEC KCSE syllabus.

Define power and calculate P = W/t; state the SI unit (watt) and convert between watts and kilowatts

Define work done by a force and calculate W = Fd cos θ; state the SI unit (joule)

Define kinetic energy (KE = ½mv²) and gravitational potential energy (GPE = mgh) and perform calculations

Identify renewable and non-renewable sources of energy

Define energy and state the law of conservation of energy; identify energy forms and transformations

Define work, kinetic energy, potential energy, and power; state their SI units and solve calculations

Work, energy and power

Sample Questions

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1
easySHORT ANSWER5 marks

State the energy transformation that takes place in each of the following: (a) An X-ray tube when fast-moving electrons are stopped by the target. (1 mark) (b) A ball bouncing on a floor. (2 marks) (c) A liquid changing into vapour. (2 marks)

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Part (a) — 1 mark
Kinetic energy → X-ray energy (electromagnetic radiation) + heat energy (1 mk)
Part (b) — 2 marks
Falling: gravitational potential energy → kinetic energy (1 mk)
Bouncing/rising: kinetic energy → gravitational PE (+ some energy lost as heat/sound) (1 mk)
Part (c) — 2 marks
Heat energy is absorbed (to overcome intermolecular forces) (1 mk)
Kinetic energy of molecules increases as they escape into the vapour phase (1 mk)
2
easySHORT ANSWER6 marks

In the study of physical sciences, understanding the fundamental concepts related to energy transfer and mechanical systems is essential. Consider the definitions and classifications that underpin these principles. (a) Define work and state its SI unit. (2 marks) (b) Define power and state its SI unit. (2 marks) (c) State the two forms of mechanical energy. (2 marks)

View Marking Scheme
Part (a) — 2 marks
Work is the product of force and distance moved in the direction of the force (1 mk)
SI unit: Joule (J) (1 mk)
Part (b) — 2 marks
Power is the rate of doing work (1 mk)
SI unit: Watt (W) (1 mk)
Part (c) — 2 marks
Kinetic energy (energy of motion) (1 mk)
Potential energy (energy of position) (1 mk)
3
easyCalculation5 marks

In the context of a student’s experience with energy transformations during physical activities, consider the concepts of energy associated with an object’s position and motion. Analyze the distinctions and calculations related to these forms of energy in the scenarios provided. (a) Distinguish between gravitational potential energy and kinetic energy. (2 marks) (b) State the formula for calculating gravitational potential energy. (1 mark) (c) A student carries a 4 kg bag to the first floor of a building, 3 m above the ground. Calculate the potential energy gained by the bag. (Take g = 10 N/kg.) (2 marks)

View Marking Scheme
Part (a) — 2 marks
Gravitational PE is energy due to position/height above a reference point (1 mk)
Kinetic energy is energy due to motion of a body (1 mk)
Part (b) — 1 mark
GPE = mgh (1 mk)
Part (c) — 2 marks
PE = mgh = 4 × 10 × 3 (1 mk)
PE = 960 J (1 mk)
4

Name two renewable sources of energy and explain why they are considered renewable. (3 marks)

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