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JEE · NEET Physics

Class 11 · Chapter 5

Work, Energy & Power

Overview, notes, short notes, formula sheet, daily practice problems, previous year questions, and videos for this chapter — all in one place.

Work, Energy & Power JEE Notes

4 min read

Fully worked, multi-step problems on variable forces, spring-block energy conservation, potential energy curves, and friction combined with energy methods — the layered setups JEE Main and JEE Advanced actually test, beyond the single-formula questions in the regular DPP.

Illustration 1 — Work Done by a Variable Force via Integration

A force F = (3x² + 2x) N acts on a body along the x-axis. Find the work done as it moves from x = 1 m to x = 3 m.

Illustration 2 — Block Dropped onto a Vertical Spring

A 2 kg block is dropped from a height of 0.4 m above the top of a vertical spring (k = 2000 N/m). Find the maximum compression of the spring. (g = 10 m/s²)

Illustration 3 — Power When Both Force and Velocity Vary with Time

A force F = 2t (in N) acts on a particle whose velocity is v = 3t (in m/s) at the same instant, both in the same direction. Find the instantaneous power at t = 2 s, and the total work done from t = 0 to t = 2 s.

Illustration 4 — Classifying Equilibrium from a Potential Energy Curve

The potential energy of a particle is U = 2x³ − 9x² + 12x (in joules, x in metres). Find the equilibrium positions and classify each as stable or unstable.

Illustration 5 — Work-Energy Theorem with Friction on an Incline

A 5 kg block starts from rest and slides 8 m down a rough 37° incline (μ = 0.25). Find its speed at the bottom. (sin37°≈0.6, cos37°≈0.8, g=10 m/s²)

Illustration 6 — Spring Release with Friction, Then Sliding to a Stop

A 2 kg block compresses a spring (k = 500 N/m) by 0.2 m against a rough surface (μ = 0.25) and is released. Find (a) its speed when the spring returns to natural length, and (b) how much FURTHER it slides before stopping completely. (g = 10 m/s²)

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