- Dr.Sanjaykumar Pawar
 |
| Force acting at an angle θ on a block producing displacement d: visualization of work done in physics. |
- Dr.Sanjaykumar Pawar
📘 WORK – CLASS 11 PHYSICS (CBSE QUESTION BANK)
🔹 1. VERY SHORT ANSWER QUESTIONS (1 Mark)
Q1. What is work in physics?
Ans: Work is done when a force produces displacement in the direction of force.
Q2. Write SI unit of work.
Ans: Joule (J)
Q3. Is work scalar or vector?
Ans: Scalar quantity
Q4. When is work done zero?
Ans: When force and displacement are perpendicular.
Q5. Write formula of work.
Ans: W = F d cosθ
🔹 2. SHORT ANSWER QUESTIONS (2–3 Marks)
Q1. State conditions when work done is zero.
Ans: Work is zero when:
- Displacement = 0
- Force = 0
- Force ⟂ displacement (θ = 90°)
Q2. Differentiate positive and negative work.
Ans:
- Positive work: force helps motion (0°–90°)
- Negative work: force opposes motion (90°–180°)
Q3. Why is work done by gravity zero in horizontal motion?
Ans: Because gravitational force acts vertically while displacement is horizontal, so θ = 90°.
Q4. Explain why holding a weight does no work.
Ans: Because displacement is zero even though force is applied.
🔹 3. LONG ANSWER QUESTIONS (5 Marks)
Q1. Derive expression for work done by constant force.
Ans:
- A constant force F acts at angle θ
- Displacement = d
- Component of force along displacement = F cosθ
- Work done = force × displacement in direction
W = F \cosθ \cdot d
Hence,
W = F d cosθ
Q2. Explain types of work with examples.
Ans:
- Positive work → pushing a box
- Negative work → friction
- Zero work → circular motion (gravity in orbit)
🔹 4. MCQs (Multiple Choice Questions)
Q1. Work done is zero when angle is:
A) 0°
B) 45°
C) 90°
D) 180°
Ans: C
Q2. SI unit of work is:
A) Newton
B) Joule
C) Watt
D) Pascal
Ans: B
Q3. Work done by friction is:
A) Positive
B) Zero
C) Negative
D) Infinite
Ans: C
Q4. Work is:
A) Vector
B) Scalar
C) Both
D) None
Ans: B
Q5. Formula of work is:
A) F/d
B) F + d
C) F d cosθ
D) F²d
Ans: C
🔹 5. ASSERTION AND REASON
Q1.
Assertion (A): Work done by centripetal force in circular motion is zero.
Reason (R): Force is perpendicular to displacement.
✔ Answer: Both A and R are true, and R is correct explanation.
Q2.
Assertion (A): Friction always does negative work.
Reason (R): It acts opposite to motion.
✔ Answer: Both A and R are true, and R explains A.
Q3.
Assertion (A): Work is a vector quantity.
Reason (R): It depends on direction.
✔ Answer: A is false, R is true.
🔹 6. FILL IN THE BLANKS
Q1. Work is a ______ quantity.
Ans: Scalar
Q2. SI unit of work is ______.
Ans: Joule
Q3. Work done is zero when force is ______ to displacement.
Ans: perpendicular
Q4. Work done formula is W = F d ______.
Ans: cosθ
Q5. Friction does ______ work.
Ans: negative
🔹 7. MATCH THE COLUMN
| Column A | Column B |
|---|---|
| 1. Positive work | A. θ = 90° |
| 2. Negative work | B. Force opposite motion |
| 3. Zero work | C. Force helps motion |
| 4. SI unit | D. Joule |
Answers:
1 → C
2 → B
3 → A
4 → D
🔹 8. CASE STUDY QUESTIONS
Passage:
A boy pushes a box on a rough surface. The force applied is 50 N, displacement is 10 m, and friction acts opposite to motion.
Q1. If force and displacement are in same direction, work is:
Ans: Positive
Q2. Work done by friction is:
Ans: Negative
Q3. If displacement is zero, work is:
Ans: Zero
Q4. SI unit of work is:
Ans: Joule
🔹 9. STATEMENT QUESTIONS
Q1.
Statement 1: Work depends on force and displacement.
Statement 2: Work is always positive.
✔ Answer: Statement 1 is true, Statement 2 is false.
Q2.
Statement 1: Work is zero when force is perpendicular to displacement.
Statement 2: cos90° = 0.
✔ Answer: Both statements are true.
📌 FINAL REVISION POINTS
✔ Work = F d cosθ
✔ Scalar quantity
✔ SI unit = Joule
✔ Zero work in 3 cases
✔ Positive, negative, zero work types
✔ Friction always negative
🔗 INTERNAL LINKS
/physics/work-and-energy-basics
/neet/physics-important-formulas
/class-11-physics/laws-of-motion
/physics/energy-types-and-conservation
/neet-mcqs/work-energy-questions
WORK (Physics) – NEET Level Notes
Definition of Work
Work is done when a force causes displacement of an object in the direction of force or its component. In physics, work is different from everyday meaning.
Formula of Work
W = F d cos θ
Where:
W = Work done
F = Force applied
d = Displacement
θ = Angle between force and displacement
Vector form: W = F · d (Dot product)
Important Concept
Only the component of force in the direction of displacement does work: Fcosθ is effective force.
Conditions for Zero Work
- Displacement = 0 → No work done (e.g., holding weight)
- Force = 0 → No work done
- θ = 90° → Force perpendicular to displacement (cos90° = 0)
Positive and Negative Work
- Positive Work: 0° ≤ θ < 90° (force helps motion)
- Negative Work: 90° < θ ≤ 180° (force opposes motion)
Example: Friction always does negative work.
Special Cases
- Friction force → Negative work
- Gravity in horizontal motion → Zero work
- Moon revolving around Earth (ideal circular motion) → Zero work by gravity
Work and Energy Relation
Work and energy have same dimensions: [ML²T⁻²]
SI Unit of Work
Joule (J)
1 Joule = 1 Newton × 1 meter
Meaning: When a force of 1 N moves an object by 1 m in direction of force.
Summary Table
| Condition | Work Done |
|---|---|
| Force in direction of motion | Positive |
| Force opposite to motion | Negative |
| Force perpendicular to motion | Zero |
| No displacement | Zero |
Key NEET Points
- Work is a scalar quantity
- Depends on angle between force and displacement
- No displacement means no work
- Friction always does negative work
- Work = energy transfer
WORK (Physics) – Mind Map Tree
WORK
│
├── Definition
│ ├─ Force causes displacement
│ ├─ W = F d cosθ
│ └─ Dot product: W = F · d
│
├── Conditions
│ ├─ Displacement = 0 → No work
│ ├─ Force = 0 → No work
│ └─ θ = 90° → No work (perpendicular)
│
├── Types of Work
│ ├─ Positive Work (0° to 90°)
│ ├─ Negative Work (90° to 180°)
│ └─ Zero Work
│
├── Special Cases
│ ├─ Friction → Negative work
│ ├─ Gravity (horizontal motion) → Zero work
│ └─ Circular motion → Zero work (ideal case)
│
├── Formula Factors
│ ├─ Force (F)
│ ├─ Displacement (d)
│ └─ Angle (θ)
│
├── Relation
│ ├─ Work = Energy transfer
│ └─ Same dimension: [ML²T⁻²]
│
├── Unit
│ ├─ SI Unit: Joule (J)
│ └─ 1 J = 1 N × 1 m
│
└── Key Points
├─ Scalar quantity
├─ Depends on angle
├─ No displacement → no work
└─ Friction always negative
