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Work and Energy — Question 14

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Question 14

An electric heater is rated 1500 W. How much energy does it use in 10 hours?

Answer

Given,

Power of the heater = 1500 W

Converting W to kW

1000 W = 1 kW

So, 1500 W = 15001000\dfrac{1500}{1000} = 1.5 kW

Time taken = 10 h

We know,

Power = Energy consumedTime taken\dfrac{\text{Energy consumed}}{\text{Time taken}}

Or

Energy consumed = Power x Time taken

Substituting we get,

Energy consumed = 1.5 x 10 = 15 kWh

Converting kWh to J

1 kWh = 3.6 x 106 J

So, 15 kWh = 3.6 x 106 x 15 = 5.4 x 107 J

Hence, the energy consumed = 5.4 x 107 J

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Science | Chapter 10: Work and EnergyWeb Content — Quick Reference

Chapter 10: Work and Energy — Quick Reference

work kinetic energy potential energy conservation of energy power kWh

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
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