6
Question Question 6
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
No. When the body falls from a height, its potential energy changes into kinetic energy progressively. A decrease in the potential energy is equal to an increase in the kinetic energy of the body. Hence, throughout the process, the total mechanical energy of the body remains conserved.
Hence, the law of conservation of energy is not violated.
BRIGHT TUTORIALS
BRIGHT TUTORIALS
CBSE Class IX | Academic Year 2026-2027
9403781999
Excellence in Education
Science | Chapter 10: Work and EnergyWeb Content — Quick Reference
Chapter 10: Work and Energy — Quick Reference
Quick Revision Points
- Work W = Fs cosθ (joule); W = 0 when F ⊥ s or displacement = 0
- KE = ½mv²; PE = mgh; Work-energy theorem: W = ΔKE
- Conservation: energy transforms but total remains constant; PE + KE = constant in free fall
- Power P = W/t (watt = J/s); 1 HP = 746 W
- 1 kWh = 3.6 × 10⁶ J = 1 unit of electricity
Exam Tips for Chapter 10
- Read the detailed chapter notes for complete coverage of all NCERT topics.
- Practice all NCERT in-text and back exercise questions — they are frequently asked in exams.
- Focus on comparison tables, diagrams, and definitions — these are high-scoring areas.
- For numericals (if applicable), practice at least 20 problems of varying difficulty.
- Refer to the practice question bank (200+ questions) for thorough preparation.
Related Resources
- Detailed Notes: ch10-work-and-energy.html
- Practice Questions: 100+ questions with answers in 05-practice-questions/
- Chapter Test: 30-mark test paper in 06-tests/chapter-tests-30marks/
- Formula Sheet: Complete formula reference in 03-teacher-aid/formula-sheet.html