JEE Main Physics Work, Energy & Power 2027: Collisions, Springs & Vertical Circles
Master the work-energy theorem, spring energy, vertical circle conditions and collisions with worked examples. A high-scoring chapter when your concepts are clean.
Edurack
September 28, 2026
When force and time are hard to track, energy is the shortcut. One equation, no vectors, no components. Work, Energy & Power rewards students who know exactly which conservation law applies to which situation, and punishes those who guess.
Momentum is conserved in every collision. Kinetic energy only in elastic ones.
Chapter at a Glance
| Snapshot | Detail |
|---|---|
| NTA unit | Unit 4 of 20 — Work, Energy & Power |
| Priority (trend-based) | High |
| Typical question style | Energy-conservation numericals, spring and collision MCQs |
| Best first step | Learn when energy is conserved and when only momentum is |
Priority reflects past-paper trends, not an official NTA weightage.
What the NTA Syllabus Covers
- Work done by a constant and a variable force, kinetic and potential energy
- Work-energy theorem, power, potential energy of a spring
- Conservation of mechanical energy, conservative and non-conservative forces
- Motion in a vertical circle, elastic and inelastic collisions in one and two dimensions
Master These Topics
1. Work-Energy Theorem and Springs
Work done by all forces equals change in kinetic energy: W_net = ΔKE. For a variable force, work is the area under the F-x graph, or ∫F dx.
A spring stores U = ½kx². Worked example: A 2 kg block compresses a spring (k = 200 N/m) by 0.1 m and is released on a smooth surface. Stored energy = ½ × 200 × 0.01 = 1 J. All of it becomes kinetic: ½ × 2 × v² = 1, so v = 1 m/s.
Power is the rate of work: P = W/t = F · v. A car engine delivering constant power has decreasing force as speed rises.
Trap: Friction is non-conservative, so mechanical energy is not conserved when it acts. Include the work done by friction explicitly in the energy equation.
2. Vertical Circle: The Two Speeds to Remember
For a mass on a string of length r moving in a vertical circle:
- At the top, the minimum speed to keep the string taut is
v_top = √(gr). - Energy conservation between bottom and top then gives the minimum speed at the bottom:
v_bottom = √(5gr).
Worked example: r = 0.5 m, g = 10. The minimum speed at the bottom is √(5 × 10 × 0.5) = √25 = 5 m/s. At the top, the minimum speed is √(10 × 0.5) ≈ 2.2 m/s.
3. Collisions: Elastic vs Inelastic
In every collision, total momentum is conserved. Kinetic energy is conserved only in elastic collisions.
- Elastic, equal masses: the bodies exchange velocities.
- Perfectly inelastic: the bodies stick together,
v = (m₁u₁ + m₂u₂) / (m₁ + m₂). - Coefficient of restitution:
e = (speed of separation) / (speed of approach), with e = 1 for elastic and e = 0 for perfectly inelastic.
Worked example: A 2 kg block at 6 m/s hits a stationary 4 kg block and they stick. Final speed = 12 / 6 = 2 m/s. Initial KE = ½ × 2 × 36 = 36 J, final KE = ½ × 6 × 4 = 12 J. So 24 J (two thirds) is lost as heat and deformation.
Common Traps to Avoid
- Applying conservation of mechanical energy when friction or air drag is present.
- Assuming kinetic energy is conserved in every collision.
- Using √(gr) at the bottom of a vertical circle instead of √(5gr).
- Forgetting that work done by a force perpendicular to displacement is zero.
60-Second Revision Sheet
W_net = ΔKE,P = F · v- Spring energy
½kx² - Vertical circle:
v_top = √(gr),v_bottom = √(5gr) - Perfectly inelastic:
v = (m₁u₁ + m₂u₂)/(m₁ + m₂)
Your Study Plan
- Day 1: work by variable forces and the work-energy theorem.
- Day 2: springs and conservation of mechanical energy with friction.
- Day 3: vertical circle and pendulum problems.
- Day 4: one-dimensional and two-dimensional collisions, timed set.
Practice Work, Energy & Power Questions Free → (opens in a new tab)
Continue Your Physics Journey
- Previous chapter: Laws of Motion
- Next chapter: Rotational Motion
- All 20 JEE Main Physics chapters
- Complete JEE Main Syllabus 2027 guide
Frequently Asked Questions
Is Work, Energy and Power scoring for JEE Main?
Yes. It is a consistent, high-yield chapter because problems reduce to one or two clean equations once you choose the right conservation law.
How do I decide between energy and Newton's laws?
If the question asks about speeds at different positions and you do not need time or acceleration, use energy. If it asks for acceleration or tension at an instant, use Newton's laws.