The minute hand completes 1.5 revolutions in 90 minutes. Distance = 1.5 × 2π × 7 = 21π cm. Displacement = 14 cm. Average speed = 21π/5400 cm s⁻¹ and average velocity = 14/5400 cm s⁻¹ downward.
Rohan studies science from 6 PM to 7:30 PM at home. Consider the tip of the minute’s hand of the wall clock. During the given time interval, what is its: (i) distance travelled, (ii) displacement, (iii) speed and (iv) velocity. The length of the minute’s hand is 7 cm (Fig. 4.32).
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The minute hand has radius 7 cm and moves for 90 minutes = 5400 s. It completes 1.5 revolutions. Therefore, distance = 1.5 × 2π × 7 = 21π cm ≈ 66 cm. After 1.5 revolutions, the tip is opposite its starting point, so displacement = 14 cm downward. Average speed = 21π/5400 ≈ 0.0122 cm s⁻¹, while average velocity = 14/5400 ≈ 0.0026 cm s⁻¹ downward.
For more NCERT Solutions of Class 9 Science Exploration Chapter 4 Describing Motion Around Us Question Answer (2026-27)
https://www.tiwariacademy.com/ncert-solutions/class-9/science/exploration-chapter-4/