The least count of a vernier calliper is 0.01 cm. A measurement should be recorded as MCQ with Answer and Explanation

Explanation:
Time period T = 1/f = 1/200 = 0.005 s = 5 ms. Frequency is number of cycles per second. Relationship T = 1/f is fundamental. For 200 Hz, period is 5 milliseconds.

Explanation:
Newton's first law (law of inertia) states bodies remain at rest or uniform motion unless acted upon by external force. This defines inertia - resistance to change in motion state. Force is defined in second law; momentum conservation in third. Memory aid: 'First law = inertia; second = F=ma; third = action-reaction'. Fundamental concept frequently tested to assess basic mechanics understanding.

Explanation:
Number of half-lives n = 15/5 = 3. Fraction = (1/2)³ = 1/8. Exponential decay: N = N₀(1/2)^(t/T). Memory aid: 'After n half-lives: fraction = 1/2ⁿ'. Radioactivity calculation frequently tested in competitive exams with simple half-life arithmetic.