Assertion (A): The coefficient of kinetic friction is always strictly less than the coefficient of limiting static friction. Reason (R): Once motion starts, the inertia of rest is broken and interlocking of surface irregularities is less effective.
A.A is false but R is true.
B.Both A and R are true but R is NOT the correct explanation of A.
C.Both A and R are true and R is the correct explanation of A.
Explanation:
Static friction opposes impending motion, reaching a maximum called limiting friction. Once the object moves, it doesn't have enough time for the microscopic irregularities (asperities) of the two surfaces to interlock strongly. Thus, the force required to keep it moving (kinetic friction) is slightly less than the force required to start the motion.
Explanation:
Spherical mirrors: f = R/2 under paraxial approximation. Derived from geometry of reflection. Memory tip: 'Mirror: f = R/2; sign: concave +, convex -'. Optics formula frequently tested in competitive exams.
Explanation:
Light year: distance light travels in one year in vacuum ≈ 9.46×10¹⁵ m. Astronomical distance unit, not time. Memory aid: 'Light year = speed × time = distance'. Unit knowledge frequently tested in competitive exams to avoid common misconception about light year being time unit.
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