Equilibrium on a Rough Horizontal Plane

Applied Mathematics — Second Secondary

Common mistakes

Comparison aspect	Main idea	Keywords
Mistake	assuming that friction always equals μR even when the body is at rest and the applied force is small. Correct: static friction equals the applied force and is at most μR it reaches μR only when the body is on the point of moving	assumingfrictionalwaysequals
Mistake	forgetting that the vertical component of an upward inclined force reduces the normal reaction. Correct: R = W − P sin θ for an upward pull	forgettingverticalcomponentupward
Mistake	drawing friction in the direction of motion instead of opposite to it. Correct: friction opposes the motion or the tendency to move	drawingfrictiondirectionmotion
Mistake	using the mass in place of the weight when calculating R. Correct: R = W = mass × g when there is no other vertical force	usingmassplaceweight

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