Mirage is an optical illusion observed in hot deserts. It is entirely caused by: MCQ with Answer and Explanation

Explanation:
Internal forces cancel in pairs (third law), so net external force = 0 ⇒ dp/dt = 0 (second law) ⇒ momentum constant. Memory aid: 'Momentum conservation ⇔ no external force ⇔ action-reaction pairs'. Mechanics foundation frequently tested in competitive exams.

Explanation:
p = mv ⇒ λ = h/(mv) ⇒ λ ∝ 1/v for constant mass. Higher velocity ⇒ shorter wavelength. Memory tip: 'λ = h/mv; faster particle ⇒ smaller wavelength'. Quantum mechanics relation frequently tested in competitive modern physics sections.

Explanation:
In uniform circular motion, speed is constant but velocity direction changes continuously, requiring centripetal acceleration directed toward the center (a = v²/r). By Newton's second law, a centripetal force must act. Velocity isn't constant (direction changes); acceleration isn't zero; force is required. Memory tip: 'Uniform circular motion: constant speed, changing velocity, center-seeking acceleration'. This conceptual question tests understanding of circular dynamics, crucial for mechanics in competitive exams. Always distinguish speed (scalar) from velocity (vector) in motion analysis.