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Physics/ Class XI/ Work, Energy and Power
KCET · Physics · Unit IV: Work, Energy and Power

Work, Energy and Power

This module focuses on work done by a force, kinetic energy, potential energy, power, conservation of mechanical energy, spring energy and one-dimensional collisions. The emphasis is on formula fluency, energy reasoning and KCET-speed problem solving.

10 Guided Questions 4 Coach Numericals 10 Chapter Check Qs 3 Dynamic Patterns
8 Key Formulas
Your Learning Path — follow in order
Step 1
💡
Learn
Concept capsule, formulas & common traps
5–10 min
Step 2
🔬
Visualise
Simulation Lab — visualise the concept
5–8 min
Step 3
✏️
Practise
Guided Practice with step-wise nudges
15–20 min
Step 4
⚡
Drill
Speed Drill + Pattern Mastery Engine
10–15 min
Step 5
🎯
Test
Chapter Check with skill-wise feedback
20 min
🧑‍🏫 Coach Mode — deep numericals 🔁 Pattern Mastery Engine ⬇ Formula Sheet PDF
Energy and Collision Simulation Lab
🔬 Live Simulation
💡 KCET tip: Explore spring energy conservation and one-dimensional collisions using interactive simulations.

Concept Capsule

  • Work is done when a force produces displacement in its direction.
  • Work is a scalar quantity and its SI unit is joule.
  • Positive work increases the energy of a body; negative work removes energy.
  • Kinetic energy is the energy possessed by a body due to its motion.
  • Gravitational potential energy near the Earth is mgh.
  • Elastic potential energy stored in a spring is 1/2 kx².
  • Power is the rate of doing work or rate of energy transfer.
  • The work-energy theorem states that net work done equals change in kinetic energy.
  • In conservation of mechanical energy, KE and PE transform into each other while total mechanical energy remains constant.
  • In collisions, momentum is conserved. In elastic collisions, kinetic energy is also conserved.

Which Formula Should I Use?

\[W=Fs\cos\theta\]

Use when: Force, displacement and angle between them are given.

Watch out: Use cosθ. If force and displacement are perpendicular, work done is zero.

\[K=\frac{1}{2}mv^2\]

Use when: Mass and speed are given and kinetic energy is asked.

Watch out: Velocity is squared, so doubling speed makes kinetic energy four times.

\[U=mgh\]

Use when: A body is raised to a height near Earth's surface.

Watch out: Use height change, not total distance travelled.

\[U=\frac{1}{2}kx^2\]

Use when: Spring compression or extension is given.

Watch out: Do not forget the factor 1/2 and square of extension.

\[P=\frac{W}{t}\]

Use when: Work done and time are given.

Watch out: Power is rate, not total work.

\[m_1u_1+m_2u_2=m_1v_1+m_2v_2\]

Use when: One-dimensional collision questions are asked.

Watch out: Use signs of velocity carefully.

Common KCET Traps

  • Using W = Fs even when force and displacement are at an angle.
  • Forgetting that work is zero when force is perpendicular to displacement.
  • Forgetting the square in kinetic energy and spring potential energy.
  • Confusing energy and power.
  • Assuming kinetic energy is conserved in all collisions.
  • Ignoring direction signs in one-dimensional collision problems.

Downloads for Revision

Formula Sheet and Key Points

A Work, Energy and Power revision PDF will be added after the first content review.

⬇ Download PDF