3
Question Question 3
The kinetic energy of an object of mass m, moving with a velocity of 5 ms-1 is 25 J. What will be its kinetic energy when its velocity is doubled? What will be its kinetic energy when its velocity is increased three times?
Given,
Kinetic Energy (KE) = 25 J
Velocity (v) = 5 ms-1
We know,
Kinetic Energy (KE) = mv2.
Substituting we get,
25 = x m x 52
25 x 2 = 25 x m
m =
m = 2 kg
When velocity is doubled :
v' = 10 ms-1
m = 2 kg
Substituting we get,
KE = x 2 x 102
K.E. = 100 J
When velocity is increased three times, then
v'' = 15 ms-1
m = 2 kg
Substituting we get,
KE = x 2 x 152
K.E. = 225 J
Hence, Kinetic Energy becomes 100 J when velocity is doubled and it becomes 225 J when velocity is increased three times.
BRIGHT TUTORIALS
BRIGHT TUTORIALS
CBSE Class IX | Academic Year 2026-2027
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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