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Work and Energy — Class 9 CBSE Science MCQs with Solutions
Free Class 9 CBSE Science Work and Energy MCQs with step-by-step solutions. Practise online on Prepizo — no login needed.
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Sample questions with solutions
Q1 — easy
Work done by a force is NEGATIVE when direction of displacement is:
A. Same as force
B. Opposite to direction of force (180°) ✓ Correct
C. Perpendicular (90°)
D. Zero
Solution: Opposite displacement gives negative work (e.g. friction).
Q2 — easy
Work done by gravitational force on a satellite moving in a circular orbit around Earth is:
A. Positive
B. Zero (force perpendicular to motion) ✓ Correct
C. Negative
D. Infinite
Solution: Gravity acts perpendicularly to orbital velocity, so work = 0.
Q3 — easy
Kinetic Energy (Eₖ) possessed by an object of mass m moving with velocity v is:
A. m·v
B. ½ m v² ✓ Correct
C. m·g·h
D. ½ m² v
Solution: Kinetic Energy = ½ m v².
Q4 — easy
Gravitational Potential Energy (Eₚ) of a mass m raised to height h above ground is:
A. m·v
B. m·g·h ✓ Correct
C. ½ m v²
D. m·g/h
Solution: Potential Energy = m g h.
Q5 — easy
A body of mass 2 kg is moving with velocity 4 m/s. Its Kinetic Energy is:
A. 8 J
B. 16 J ✓ Correct
C. 32 J
D. 4 J
Solution: Eₖ = ½(2)(4²) = 16 J.
Q6 — easy
Law of Conservation of Energy states that total energy of an isolated system:
A. Decreases continually
B. Increases
C. Remains constant (transformed from one form to another) ✓ Correct
D. Drops to zero
Solution: Energy can neither be created nor destroyed, only transformed.
Q7 — easy
Rate of doing work or rate of transfer of energy is defined as:
A. Force
B. Momentum
C. Power ✓ Correct
D. Pressure
Solution: Power = Work / Time.
Q8 — easy
SI unit of Power is Watt (W), which is equivalent to:
A. 1 J·s
B. 1 Joule per second (1 J/s) ✓ Correct
C. 1 N·m
D. 1 kg·m/s²
Solution: 1 Watt = 1 J/s.
Q9 — easy
Commercial unit of electrical energy used in electricity bills is:
A. Joule
B. Kilowatt-hour (kWh) ✓ Correct
C. Watt-hour
D. Horsepower
Solution: 1 kWh = 1 commercial unit of electricity.
Q10 — easy
When a free-falling body drops from a height, its potential energy converts into:
A. Heat energy
B. Kinetic energy ✓ Correct
C. Sound energy
D. Chemical energy
Solution: Potential energy decreases while kinetic energy increases by equal amount.
Q11 — easy
1 Horsepower (HP) is equal to approximately how many Watts?
A. 500 W
B. 746 W ✓ Correct
C. 1000 W
D. 100 W
Solution: 1 HP = 746 Watts.
Q12 — medium
Scientific work is said to be done when an applied force causes:
A. Fatigue
B. Displacement of object in direction of force ✓ Correct
C. Heating
D. Pressure
Solution: Work = Force × Displacement in direction of force.
Q13 — medium
SI unit of Work and Energy is:
A. Newton (N)
B. Joule (J) ✓ Correct
C. Watt (W)
D. Pascal (Pa)
Solution: 1 Joule = 1 N × 1 m.
Q14 — medium
Convert 1 kWh into Joules:
A. 3.6 × 10⁵ J
B. 3.6 × 10⁶ J ✓ Correct
C. 3.6 × 10⁷ J
D. 1000 J
Solution: 1 kWh = 1000 W × 3600 s = 3.6 × 10⁶ J.
Q15 — medium
If a crane lifts a 1000 N load through 10 m height in 20 seconds, power of crane is:
A. 500 W ✓ Correct
B. 1000 W
C. 200 W
D. 50 W
Solution: Work = 1000 × 10 = 10000 J. Power = 10000 / 20 = 500 W.