Lesson 5 – Work, Energy and Power Important Questions & Answers (Intermediate)
This section contains the most expected questions for Intermediate Physics examinations. Answers are written in a way that examiners expect.
Very Short Answer Questions (1 Mark)
Q1. What is work?
Work is said to be done when a force acting on a body produces displacement in the direction of the force.
Q2. Write the SI unit of work and energy.
The SI unit of work and energy is Joule (J).
Q3. What is zero work?
When force acts on a body but produces no displacement in the direction of the force, the work done is called zero work.
Q4. Give one example of negative work.
Work done by friction on a moving body is negative.
Short Answer Questions (2–3 Marks)
Q5. Distinguish between positive work and negative work.
| Positive Work | Negative Work |
|---|---|
| Force and displacement are in the same direction. | Force and displacement are in opposite directions. |
| Energy of the body increases. | Energy of the body decreases. |
| Example: Gravity on falling body. | Example: Friction opposing motion. |
Q6. Define kinetic energy.
The energy possessed by a body by virtue of its motion is called kinetic energy.
Q7. Write the expression for kinetic energy.
Kinetic Energy = ½ mv²
Q8. What is power?
Power is defined as the rate of doing work or the rate of transfer of energy.
Long Answer Questions (4–5 Marks)
Q9. Derive the expression for kinetic energy.
Answer:
Consider a body of mass m moving with initial velocity u. Let a constant force F act on it producing acceleration a. After displacement s, its final velocity becomes v.
From equations of motion:
v² − u² = 2as
Force, F = ma
Work done, W = Fs
W = ma × s
Substituting s = (v² − u²) / 2a
W = ½ m (v² − u²)
If the body starts from rest, u = 0
W = ½ mv²
This work done is equal to the kinetic energy of the body.
Q10. State and explain the work–energy theorem.
Answer:
The work–energy theorem states that the work done by the net force acting on a body is equal to the change in its kinetic energy.
Mathematically,
W = ΔK
This theorem is useful in solving problems where force and displacement vary continuously.
Numerical Problems (Very Important)
Q11. Find the kinetic energy of a body of mass 2 kg moving with a velocity of 10 m/s.
Solution:
Given:
m = 2 kg
v = 10 m/s
Kinetic Energy = ½ mv²
= ½ × 2 × (10)²
= 100 J
Answer: Kinetic energy = 100 J
Q12. A force of 10 N acts on a body and produces a displacement of 5 m in the direction of force. Find the work done.
Solution:
W = Fs
= 10 × 5
= 50 J
Answer: Work done = 50 J
Important Exam Tips
- Always write formulas before substitution.
- Use proper units.
- Draw simple diagrams if required.
- Do not skip derivation steps.
“Understanding energy makes mechanics simple.”
Work, Energy & Power – Complete Physics Library
This is the MASTER LIBRARY PAGE for the complete chapter Work, Energy and Power, prepared for Intermediate, IIT-JEE (Main & Advanced), NEET and competitive exams.
All concepts are explained from basic to IIT level, including theory, derivations, numerical problems, objective questions, previous year questions, tough IIT problems, tricks and cautions.
📚 Complete Lesson Index (Part 1 – Part 39)
- Part 1 – Introduction to Work
- Part 2 – Types of Work
- Part 3 – Variable Force & Graphs
- Part 4 – Kinetic Energy
- Part 5 – Work–Energy Theorem
- Part 6 – Potential Energy
- Part 7 – Conservative Forces
- Part 8 – Mechanical Energy
- Part 9 – Power
- Part 10 – Power Applications
- Part 11
- Part 12
- Part 13
- Part 14
- Part 15
- Part 16
- Part 17
- Part 18
- Part 19
- Part 20
- Part 21
- Part 22
- Part 23
- Part 24
- Part 25
- Part 26
- Part 27
- Part 28
- Part 29
- Part 30
- Part 31
- Part 32
- Part 33
- Part 34
- Part 35
- Part 36
- Part 37
- Part 38
- Part 39 – Final IIT Tough Problems & Solutions
Prepared by: Shaktimatha Learning 🌱
Strong Concepts • Smart Practice • Exam Success
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