Work, Energy & Power
Q. A 10 kg object is dropped from a height of 20 m. What is its potential energy at the top? (g = 9.8 m/s²) (1960)
A.
196 J
B.
98 J
C.
294 J
D.
490 J
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Solution
Potential Energy (PE) = mgh = 10 kg × 9.8 m/s² × 20 m = 1960 J.
Correct Answer: C — 294 J
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Q. A 10 kg object is lifted to a height of 2 m. What is the work done against gravity? (g = 9.8 m/s²)
A.
196 J
B.
98 J
C.
20 J
D.
39.2 J
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Solution
Work done (W) = m × g × h = 10 kg × 9.8 m/s² × 2 m = 196 J.
Correct Answer: A — 196 J
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Q. A 10 N force is applied to move an object 3 m. What is the work done if the force is applied at an angle of 60 degrees to the direction of motion?
A.
15 J
B.
30 J
C.
25 J
D.
20 J
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Solution
Work done = Force × Distance × cos(θ) = 10 N × 3 m × cos(60°) = 10 N × 3 m × 0.5 = 15 J
Correct Answer: A — 15 J
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Q. A 1000 kg car is moving at a speed of 15 m/s. What is its kinetic energy?
A.
112,500 J
B.
75,000 J
C.
50,000 J
D.
25,000 J
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Solution
Kinetic Energy = 0.5 * m * v² = 0.5 * 1000 kg * (15 m/s)² = 112,500 J.
Correct Answer: A — 112,500 J
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Q. A 1000 kg car is moving at a speed of 36 km/h. What is its kinetic energy? (1 km/h = 1/3.6 m/s) (2000)
A.
500 J
B.
1000 J
C.
2000 J
D.
5000 J
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Solution
First convert speed: 36 km/h = 10 m/s. KE = 0.5 × m × v² = 0.5 × 1000 kg × (10 m/s)² = 0.5 × 1000 × 100 = 50000 J.
Correct Answer: C — 2000 J
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Q. A 15 kg object is lifted to a height of 4 m. What is the work done against gravity? (g = 9.8 m/s²) (2021)
A.
588 J
B.
5880 J
C.
392 J
D.
294 J
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Solution
Work = mgh = 15 kg * 9.8 m/s² * 4 m = 588 J.
Correct Answer: A — 588 J
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Q. A 2 kg object is lifted to a height of 5 m. What is the potential energy gained by the object? (2022)
A.
10 J
B.
20 J
C.
30 J
D.
40 J
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Solution
Potential Energy = mass × g × height = 2 kg × 10 m/s² × 5 m = 100 J
Correct Answer: B — 20 J
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Q. A 2 kg object is lifted to a height of 5 m. What is the potential energy gained by the object? (g = 9.8 m/s²)
A.
98 J
B.
19.6 J
C.
39.2 J
D.
49 J
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Solution
Potential Energy = mass × g × height = 2 kg × 9.8 m/s² × 5 m = 98 J
Correct Answer: A — 98 J
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Q. A 3 kg object is dropped from a height of 10 m. What is the potential energy at the top? (2022)
A.
30 J
B.
60 J
C.
90 J
D.
120 J
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Solution
Potential Energy = mass × g × height = 3 kg × 10 m/s² × 10 m = 300 J
Correct Answer: C — 90 J
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Q. A 4 kg object is lifted to a height of 2 m. What is the work done against gravity? (2022)
A.
40 J
B.
80 J
C.
20 J
D.
60 J
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Solution
Work done = mass × g × height = 4 kg × 10 m/s² × 2 m = 80 J
Correct Answer: B — 80 J
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Q. A 5 kg object is dropped from a height of 10 m. What is its potential energy at the top? (g = 9.8 m/s²)
A.
490 J
B.
98 J
C.
50 J
D.
100 J
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Solution
Potential Energy = mgh = 5 kg * 9.8 m/s² * 10 m = 490 J.
Correct Answer: A — 490 J
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Q. A 5 kg object is dropped from a height of 10 m. What is its speed just before it hits the ground? (g = 9.8 m/s²)
A.
14 m/s
B.
20 m/s
C.
10 m/s
D.
15 m/s
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Solution
Using energy conservation, Potential Energy = Kinetic Energy at the ground: mgh = 0.5mv²; v = √(2gh) = √(2 × 9.8 m/s² × 10 m) = 14 m/s
Correct Answer: A — 14 m/s
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Q. A car accelerates from rest to a speed of 20 m/s. If its mass is 1000 kg, what is the kinetic energy of the car at this speed? (2000)
A.
200 J
B.
1000 J
C.
2000 J
D.
4000 J
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Solution
Kinetic Energy (KE) = 0.5 × m × v² = 0.5 × 1000 kg × (20 m/s)² = 0.5 × 1000 × 400 = 200000 J.
Correct Answer: C — 2000 J
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Q. A car of mass 1000 kg accelerates from rest to a speed of 20 m/s. What is the kinetic energy gained?
A.
200,000 J
B.
100,000 J
C.
50,000 J
D.
20,000 J
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Solution
Kinetic Energy = 0.5 * m * v² = 0.5 * 1000 kg * (20 m/s)² = 200,000 J.
Correct Answer: B — 100,000 J
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Q. A cyclist does 1500 J of work to climb a hill. If he takes 5 minutes, what is his average power output?
A.
5 W
B.
10 W
C.
15 W
D.
20 W
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Solution
Power = Work / Time = 1500 J / (5 * 60 s) = 5 W.
Correct Answer: B — 10 W
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Q. A cyclist does 600 J of work to climb a hill. If he takes 30 seconds, what is his average power output? (2022)
A.
10 W
B.
20 W
C.
30 W
D.
40 W
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Solution
Power = Work / Time = 600 J / 30 s = 20 W.
Correct Answer: B — 20 W
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Q. A cyclist is moving at a speed of 15 m/s. If the total mass of the cyclist and the bicycle is 75 kg, what is the kinetic energy?
A.
843.75 J
B.
562.5 J
C.
1687.5 J
D.
1125 J
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Solution
Kinetic Energy (KE) = 0.5 × m × v² = 0.5 × 75 kg × (15 m/s)² = 0.5 × 75 × 225 = 8437.5 J.
Correct Answer: A — 843.75 J
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Q. A force of 10 N is applied to move a box 5 m across a floor. What is the work done on the box?
A.
10 J
B.
20 J
C.
50 J
D.
5 J
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Solution
Work done = Force × Distance = 10 N × 5 m = 50 J
Correct Answer: B — 20 J
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Q. A force of 10 N is applied to move a box 5 m across a floor. What is the work done by the force?
A.
10 J
B.
20 J
C.
50 J
D.
5 J
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Solution
Work done = Force × Distance = 10 N × 5 m = 50 J
Correct Answer: B — 20 J
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Q. A force of 10 N is applied to move a box 5 m along a horizontal surface. What is the work done by the force? (2021)
A.
20 J
B.
50 J
C.
10 J
D.
5 J
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Solution
Work done = Force × Distance = 10 N × 5 m = 50 J
Correct Answer: B — 50 J
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Q. A force of 10 N is applied to move an object 5 m in the direction of the force. What is the work done by the force?
A.
10 J
B.
20 J
C.
50 J
D.
5 J
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Solution
Work done (W) = Force (F) × Distance (d) × cos(θ). Here, θ = 0° (force and displacement are in the same direction). W = 10 N × 5 m × cos(0°) = 10 N × 5 m = 50 J.
Correct Answer: B — 20 J
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Q. A force of 20 N is applied at an angle of 60° to the horizontal while moving an object 4 m. What is the work done?
A.
40 J
B.
80 J
C.
20 J
D.
60 J
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Solution
Work done (W) = F × d × cos(θ) = 20 N × 4 m × cos(60°) = 20 × 4 × 0.5 = 40 J.
Correct Answer: B — 80 J
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Q. A force of 50 N is applied to move an object 4 m. How much work is done?
A.
100 J
B.
150 J
C.
200 J
D.
250 J
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Solution
Work = Force * Distance = 50 N * 4 m = 200 J.
Correct Answer: C — 200 J
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Q. A machine does 1200 J of work in 60 seconds. What is its efficiency if the input energy is 2000 J? (2022)
A.
60%
B.
70%
C.
80%
D.
90%
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Solution
Efficiency = (Output Work / Input Energy) * 100 = (1200 J / 2000 J) * 100 = 60%.
Correct Answer: A — 60%
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Q. A machine does 1500 J of work in 30 seconds. What is its power output?
A.
50 W
B.
30 W
C.
75 W
D.
100 W
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Solution
Power (P) = Work (W) / Time (t). P = 1500 J / 30 s = 50 W.
Correct Answer: A — 50 W
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Q. A person lifts a 10 kg box to a height of 2 m. What is the work done against gravity? (g = 9.8 m/s²)
A.
196 J
B.
98 J
C.
20 J
D.
10 J
Show solution
Solution
Work = mgh = 10 kg * 9.8 m/s² * 2 m = 196 J.
Correct Answer: A — 196 J
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Q. An object is lifted vertically 4 m against gravity. If the mass of the object is 3 kg, what is the work done against gravity? (g = 9.8 m/s²)
A.
117.6 J
B.
29.4 J
C.
39.2 J
D.
78.4 J
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Solution
Work done (W) = mgh = 3 kg × 9.8 m/s² × 4 m = 117.6 J.
Correct Answer: A — 117.6 J
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Q. An object is moving with a speed of 15 m/s and has a mass of 3 kg. What is its kinetic energy?
A.
67.5 J
B.
45 J
C.
90 J
D.
135 J
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Solution
Kinetic Energy (KE) = 0.5 × m × v² = 0.5 × 3 kg × (15 m/s)² = 0.5 × 3 × 225 = 337.5 J.
Correct Answer: C — 90 J
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Q. How much work is done when a force of 10 N moves an object 5 m in the direction of the force?
A.
25 J
B.
50 J
C.
75 J
D.
100 J
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Solution
Work = Force * Distance = 10 N * 5 m = 50 J.
Correct Answer: B — 50 J
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Q. How much work is done when a force of 30 N moves an object 4 m in the direction of the force?
A.
120 J
B.
90 J
C.
60 J
D.
30 J
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Solution
Work = Force * Distance = 30 N * 4 m = 120 J.
Correct Answer: A — 120 J
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