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Forces and friction — KCSE Physics

KCSE Physics · 109 practice questions · 6 syllabus objectives

34 easy38 medium37 hard

What You'll Learn

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

Identify and describe the types of forces (gravitational, normal reaction, tension, friction) and distinguish mass from weight

Distinguish between static and kinetic friction and apply the formula f = μN to solve problems

Solve problems involving objects on inclined planes, taking into account the component forces

Define viscosity, explain terminal velocity and sketch relevant velocity–time graphs

State Newton’s laws of motion; define momentum and impulse; apply F = ma and conservation of momentum

Forces and friction

Sample Questions

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1
easySHORT ANSWER4 marks

A sled of mass 10 kg is sliding down a frictional incline of 20° with a coefficient of kinetic friction of 0.1. (a) State the formula for calculating the frictional force acting on the sled. (2 marks) (b) Calculate the frictional force acting on the sled. (2 marks)

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Part (a) — 2 marks
Frictional force (F_f) = μN (1 mk)
Where μ is the coefficient of kinetic friction and N is the normal force (1 mk)
Part (b) — 2 marks
Calculate normal force: N = mg cos(20°) (1 mk)
Then F_f = 0.1 × (10 kg × 9.8 m/s² × cos(20°)) ≈ 0.1 × 92.1 N = 9.21 N (1 mk)
2
easySHORT ANSWER4 marks

A block of mass 5 kg is placed on an inclined plane at an angle of 30°. (a) State the component of the gravitational force acting parallel to the incline. (2 marks) (b) Calculate this component. (2 marks)

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Part (a) — 2 marks
The component is given by mg sin(θ) (1 mk)
Where m is the mass and θ is the angle of inclination (1 mk)
Part (b) — 2 marks
Using the formula: F = mg sin(30°) (1 mk)
Substituting: F = 5 kg × 9.8 m/s² × 0.5 = 24.5 N (1 mk)
3
easySHORT ANSWER4 marks

Explain the difference between weight and mass. (4 marks)

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Part (a) — 2 marks
Mass is the amount of matter in an object (1 mk)
SI unit of mass is kilogram (kg) (1 mk)
Part (b) — 2 marks
Weight is the gravitational force acting on an object (1 mk)
SI unit of weight is newton (N) (1 mk)
4

Name two types of contact forces and give one example of each. (4 marks)

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