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Work and Energy — Question 17

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Question 17

Calculate the work required to be done to stop a car of 1500 kg moving at a velocity of 60 kmh-1.

Answer

Given,

Mass (m) = 1500 kg

Initial velocity (v) = 60 kmh-1

Final velocity = 0

Converting kmh-1 to ms-1 : multiply by 518\dfrac{5}{18}

60 x 518\dfrac{5}{18} = 503\dfrac{50}{3} ms-1

Work required to stop the moving car = Kinetic energy of car (K.E.)

K.E. = 12\dfrac{1}{2}mv2

= 12\dfrac{1}{2} x 1500 x (503)(\dfrac{50}{3})2

= 12\dfrac{1}{2} x 1500 x 25009\dfrac{2500}{9}

= 208333.3 J

Hence, work done = 208333.3 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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