NCERT • Class XI • Chapter 5

Work, Power & Energy – True/False Warm‑up

Quickly test your understanding of work, kinetic & potential energy, work–energy theorem and power before you attempt full numericals and PYQs. Designed for fast revision and error‑spotting.

🎯 Concept check: Work, Energy & Power core ideas
⏱️ 10–15 min T/F sprint
📚 Best for Boards • JEE • NEET
Start True–False Set ➜ Jump to Notes & Formulas
Energy Profile • Concept Visual Animated Hero
Emech constant (frictionless) Turning points ↔ K ↔ U

Quick chapter snapshot

Board
NCERT • CBSE • State Boards
Chapter
5 – Work, Energy & Power
Exam Weightage
~3–4 questions across Mechanics in Boards & JEE/NEET
Best use of this page
Rapid T/F drill + linked formula & notes revision
Core coverage
Work by constant & variable forces, kinetic & potential energy, work–energy theorem, conservation of mechanical energy and power.
When to use T/F
Before solving numericals, after finishing the chapter, and a day before exam as a last‑minute misconception filter.

Why this chapter matters (Boards • JEE • NEET)

Gateway topic in Mechanics
  • ➤ Work, energy and power are fundamental tools to analyse all kinds of motion and interactions, from blocks on inclines to oscillations and modern physics setups.
  • ➤ Conservation of energy is one of the most used ideas in all of Physics and appears repeatedly in JEE/NEET and board numericals.
  • ➤ Many higher topics (SHM, gravitation, electric potential, modern physics) reuse the same language of potential energy curves and energy graphs.
  • ➤ Strong grip here reduces dependence on long kinematics and lets you solve questions faster with the work–energy theorem.
Where it shows up
Common in:
Straight‑line motion with forces Inclined planes & pulleys Collisions & braking Power of engines, machines Potential energy graphs

Key concept highlights

Concept 01

Work done by a force

Work measures energy transfer when a force causes displacement; for a constant force it equals the product of force, displacement and the cosine of the angle between them.

Concept 02

Kinetic energy & W–E theorem

Kinetic energy is the energy of motion, and the work–energy theorem states that net work done on a particle equals the change in its kinetic energy.

Concept 03

Potential energy & conservative forces

Potential energy is stored energy of configuration in a conservative force field; changes in it are related to work done by conservative forces and help in using energy graphs.

Concept 04

Conservation of mechanical energy

In absence of non‑conservative work, the sum of kinetic and potential energies of a system remains constant and is very useful in free‑fall and smooth‑incline problems.

Concept 05

Power & rate of work

Power quantifies how fast work is done or energy is transferred and can be expressed as work per unit time or as the scalar product of force and velocity.

Concept 06

Variable forces & area under graphs

For variable forces, work done between two points equals the area under the force–displacement graph, a common framing in objective questions.

Important formula capsules

Work by constant force
\( W = \vec{F} \cdot \vec{s} = Fs\cos\theta \)
Work by variable force
\( W = \int_{s_1}^{s_2} \vec{F} \cdot d\vec{s} \)
Kinetic energy
\( K = \dfrac{1}{2}mv^{2} \)
Work–energy theorem
\( W_{\text{net}} = \Delta K \)
Gravitational potential energy (near Earth)
\( U = mgh \)
Mechanical energy
\( E_{\text{mech}} = K + U \)
Average power
\( P_{\text{avg}} = \dfrac{W}{\Delta t} \)
Instantaneous power
\( P = \vec{F} \cdot \vec{v} \)

What you will learn from this T/F set

  • ▹ Distinguish clearly between work being positive, negative or zero in different force–displacement situations.
  • ▹ Connect formulas of work, kinetic and potential energy to physical situations instead of memorising them blindly.
  • ▹ Use the work–energy theorem as a shortcut in straight‑line motion and block‑on‑incline problems.
  • ▹ Interpret force–displacement and energy graphs for common exam‑style questions.
  • ▹ Avoid typical misconceptions, e.g. “no displacement ⇒ no work” versus “no work by a particular force”, or “power is always constant”.

Navigate to detailed notes & practice

📘 Full chapter notes (NCERT + intuition) 📄 Formula sheet & flash revision ❓ MCQ practice set ✔️ Scroll to True–False questions

Exam strategy & preparation tips

Step 01
Fix sign & direction issues

Practise identifying the angle between force and displacement before applying \( W = Fs\cos\theta \); many wrong answers in MCQs come only from sign mistakes.

Step 02
Think in energy, not only forces

Whenever only speeds and heights are involved, try solving via conservation of energy or the work–energy theorem first; it generally reduces algebra and is faster in exams.

Step 03
Use T/F as misconception traps

Attempt this T/F set quickly, then mark statements you got wrong and revisit those exact concepts in your notes and NCERT examples for targeted correction.

Step 04
Map formulas to situations

Make a small map: which formula applies to lifting, sliding with friction, springs, circular motion and power of machines; attach 1–2 typical examples to each case.

Step 05
Revise with energy graphs

For higher‑level prep, practise reading potential‑energy curves to identify stable/unstable equilibrium and allowed regions of motion, which often appears in JEE/NEET questions.

Step 06
Close with mixed problems

Finally, attempt a mix of PYQs where work, energy and power combine with Newton’s laws and kinematics to ensure your understanding is robust across the full Mechanics toolkit.

Your Progress 0 / 25 attempted
Q 01 / 25
If a constant force acts on a body and there is no displacement, then the work done by the force is zero.
Q 02 / 25
Work done by a force can be positive, negative or zero.
Q 03 / 25
Kinetic energy of a body depends only on its speed and not on the direction of motion.
Q 04 / 25
A body can possess energy even when its mechanical work per second (power) is zero.
Q 05 / 25
The SI unit of work and the SI unit of energy are the same.
Q 06 / 25
If a force is always perpendicular to the instantaneous displacement of a particle, then the work done by the force is zero.
Q 07 / 25
When a body falls freely under gravity in vacuum, the loss in potential energy is equal to the gain in kinetic energy at every instant (neglecting relativistic effects).
Q 08 / 25
A porter walking on a level road with a load on his head does positive work against gravity.
Q 09 / 25
The area under a force–displacement graph represents the work done by that force.
Q 10 / 25
If the net work done on a particle during its motion is zero, then its speed must remain constant.
Q 11 / 25
Power is defined as the work done per unit time, so it must always be constant for a given process.
Q 12 / 25
A conservative force is one for which the work done between two points depends only on the path taken.
Q 13 / 25
The work done by all conservative forces over any closed path is zero.
Q 14 / 25
In presence of non-conservative forces (like friction), the total mechanical energy of a system is always conserved.
Q 15 / 25
A satellite moving in a perfectly circular orbit around the Earth has constant kinetic energy and constant gravitational potential energy.
Q 16 / 25
For a body attached to an ideal spring obeying Hooke's law, the potential energy stored in the spring is proportional to the square of its extension.
Q 17 / 25
A body can have non-zero momentum but zero kinetic energy in classical mechanics.
Q 18 / 25
In an elastic collision between two particles, both kinetic energy and linear momentum of the system are conserved.
Q 19 / 25
In an inelastic collision, total mechanical energy of the system decreases, but total linear momentum of the system can still remain conserved.
Q 20 / 25
A heavier body always has more kinetic energy than a lighter body if both have the same linear momentum.
Q 21 / 25
If the net external work done on a system of particles is zero, then the velocity of the centre of mass of the system must remain constant.
Q 22 / 25
A variable force whose magnitude depends on position can never be treated using the work-energy theorem.
Q 23 / 25
For a particle subjected only to a one-dimensional conservative force, the motion can be described by imagining the particle sliding in an effective potential energy curve.
Q 24 / 25
The maximum speed of a particle executing vertical motion attached to a spring (neglecting air resistance) occurs at the extreme positions where its potential energy is maximum.
Q 25 / 25
In a central gravitational field, a bound orbit with total mechanical energy just less than zero corresponds to a nearly parabolic trajectory, which is highly sensitive to small changes in energy.
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