Which of the following scenarios best illustrates conservation of momentum?
A. A car accelerating on a straight road
B. A ball falling freely under gravity
C. A book resting on a table
D. Collision between two billiard balls on a frictionless table
Answer: Option D
Solution (By JKSSB Mock Tests)
Conservation of momentum applies to isolated systems with no external forces. In billiard ball collision on frictionless table, external forces (gravity, normal) cancel vertically, and no horizontal external forces act, so horizontal momentum is conserved. Book on table has zero momentum but no dynamic process. Falling ball has external gravity force. Accelerating car has external engine force. Thus only option B represents an isolated system where momentum conservation holds. Memory aid: Momentum conserved when net external force = 0. This conceptual question tests understanding of system boundaries and force analysis, crucial for mechanics sections in competitive exams.
Explanation:
TIR: denser→rarer medium AND incidence angle > critical angle. Glass to air satisfies first condition; angle must exceed θ_c. Memory aid: 'TIR: n₁>n₂ AND i>θ_c; direction matters'. Optics condition frequently tested in competitive exams.
Explanation:
Dimensionless quantities: angle (radian = arc/radius), strain (ΔL/L), refractive index (ratio of speeds). All have [M⁰L⁰T⁰]. Memory aid: 'Ratios of same dimensions ⇒ dimensionless'. Dimensional analysis question frequently tested in competitive exams to identify dimensionless physical quantities.
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