Work and Energy Part 4: MCQs (Q76–Q100)
⚡ Work and Energy – Class 9 Science MCQs
Section 4: Numericals, Applications & HOTS (Q76–Q100)
Q76. A force of 20 N displaces a body by 5 m in direction of force. Work done = ?
A. 25 J
B. 50 J
C. 75 J
D. 100 J
✅ Correct Answer: D. 100 J
Explanation:
- W = F × d = 20 × 5 = 100 J.
Q77. A 10 kg object lifted to height 2 m. Work done = ? (g = 10 m/s²)
A. 100 J
B. 150 J
C. 200 J
D. 250 J
✅ Correct Answer: C. 200 J
Explanation:
- W = mgh = 10 × 10 × 2 = 200 J.
Q78. KE of 2 kg object moving with 4 m/s = ?
A. 8 J
B. 12 J
C. 16 J
D. 32 J
✅ Correct Answer: D. 16 J
Explanation:
- KE = ½ mv² = 0.5 × 2 × 16 = 16 J.
Q79. Work done on body = 200 J. Displacement = 4 m. Force = ?
A. 25 N
B. 50 N
C. 75 N
D. 100 N
✅ Correct Answer: B. 50 N
Explanation:
- W = Fd → F = 200/4 = 50 N.
Q80. A motor does 1000 J work in 10 s. Power = ?
A. 10 W
B. 50 W
C. 100 W
D. 200 W
✅ Correct Answer: C. 100 W
Explanation:
- P = W/t = 1000/10 = 100 W.
Q81. A body of mass 5 kg raised to 10 m. Potential energy = ? (g = 9.8)
A. 450 J
B. 490 J
C. 500 J
D. 600 J
✅ Correct Answer: B. 490 J
Explanation:
- PE = mgh = 5 × 9.8 × 10 = 490 J.
Q82. KE of body doubled, velocity becomes:
A. √2 times
B. 2 times
C. 3 times
D. 4 times
✅ Correct Answer: A. √2 times
Explanation:
- KE ∝ v² → if KE doubled, v = √2 × v.
Q83. A boy lifts 20 kg mass through 1 m in 2 s. Power = ? (g = 10)
A. 50 W
B. 100 W
C. 150 W
D. 200 W
✅ Correct Answer: B. 100 W
Explanation:
- Work = mgh = 20 × 10 × 1 = 200 J.
- Power = 200/2 = 100 W.
Q84. A ball thrown vertically up reaches 20 m. Initial velocity = ? (g = 10)
A. 10 m/s
B. 20 m/s
C. 25 m/s
D. 40 m/s
✅ Correct Answer: B. 20 m/s
Explanation:
- h = u²/2g → 20 = u²/20 → u² = 400 → u = 20.
Q85. At maximum height of projectile, KE = 20 J, PE = 80 J. Total energy = ?
A. 20 J
B. 80 J
C. 100 J
D. 120 J
✅ Correct Answer: C. 100 J
Explanation:
- Total = KE + PE = 20 + 80 = 100 J.
Q86. A car of mass 1000 kg moves at 20 m/s. KE = ?
A. 1 × 10⁵ J
B. 2 × 10⁵ J
C. 3 × 10⁵ J
D. 4 × 10⁵ J
✅ Correct Answer: B. 2 × 10⁵ J
Explanation:
- KE = ½ mv² = 0.5 × 1000 × 400 = 2 × 10⁵ J.
Q87. A machine does 500 J work in 5 s. Its power = ?
A. 50 W
B. 75 W
C. 100 W
D. 125 W
✅ Correct Answer: C. 100 W
Explanation:
- P = 500/5 = 100 W.
Q88. Energy conversion in solar cell:
A. Heat → electricity
B. Light → electricity
C. Chemical → electricity
D. Sound → electricity
✅ Correct Answer: B. Light → electricity
Q89. Work done in moving 10 C charge through 2 V = ?
A. 5 J
B. 10 J
C. 15 J
D. 20 J
✅ Correct Answer: D. 20 J
Explanation:
- Work = QV = 10 × 2 = 20 J.
Q90. Which energy conversion occurs in electric fan?
A. Electrical → mechanical
B. Electrical → heat
C. Electrical → sound
D. Electrical → chemical
✅ Correct Answer: A. Electrical → mechanical
Q91. A ball of mass 0.5 kg falls from 20 m. KE just before hitting ground = ? (g = 10)
A. 50 J
B. 100 J
C. 200 J
D. 500 J
✅ Correct Answer: B. 100 J
Explanation:
- PE lost = KE gained = mgh = 0.5 × 10 × 20 = 100 J.
Q92. Efficiency of ideal machine = ?
A. 0%
B. 50%
C. 75%
D. 100%
✅ Correct Answer: D. 100%
Q93. Work done when force applied is perpendicular to displacement = ?
A. Positive
B. Negative
C. Zero
D. Maximum
✅ Correct Answer: C. Zero
Q94. KE of moving body is directly proportional to:
A. v
B. v²
C. √v
D. 1/v
✅ Correct Answer: B. v²
Q95. A body of 2 kg dropped from 5 m. KE at ground = ? (g = 10)
A. 50 J
B. 75 J
C. 100 J
D. 150 J
✅ Correct Answer: C. 100 J
Explanation:
- KE = mgh = 2 × 10 × 5 = 100 J.
Q96. A 60 W bulb glows for 2 hours. Energy consumed = ?
A. 0.12 kWh
B. 0.2 kWh
C. 0.5 kWh
D. 1.2 kWh
✅ Correct Answer: A. 0.12 kWh
Explanation:
- E = P × t = 60/1000 × 2 = 0.12 kWh.
Q97. A man pulls cart with 200 N force through 50 m. Work = ?
A. 5000 J
B. 6000 J
C. 8000 J
D. 10000 J
✅ Correct Answer: D. 10000 J
Explanation:
- W = Fd = 200 × 50 = 10000 J.
Q98. Energy conversion in microphone:
A. Sound → electrical
B. Electrical → sound
C. Electrical → heat
D. Chemical → electrical
✅ Correct Answer: A. Sound → electrical
Q99. A battery converts:
A. Electrical → chemical
B. Chemical → electrical
C. Mechanical → electrical
D. Heat → electrical
✅ Correct Answer: B. Chemical → electrical
Q100. A hydroelectric power station converts:
A. Heat → electrical
B. Mechanical → electrical
C. Water’s PE → electrical
D. Solar → electrical
✅ Correct Answer: C. Water’s PE → electrical
Explanation:
- Water at height has PE → turbine KE → electricity.
Work and Energy Class 9, CBSE Class 9 Science MCQs, NCERT Class 9 work and energy questions, Class 9 Science exam practice, Online learning Science Class 9, work and energy class 9 science mcqs with answers, cbse class 9 science work and energy multiple choice questions, ncert class 9 work and energy quiz online, important mcqs for cbse class 9 science work and energy chapter, work and energy class 9 mcqs for online learning