Mechanics - Work, Energy & Power for Competitive Exams

Mechanics - Work, Energy & Power

Q. If a 1000 kg car is moving at a speed of 36 km/h, what is its kinetic energy? (2021)

A. 500 J
B. 1000 J
C. 2000 J
D. 3000 J

Solution

Convert speed to m/s: 36 km/h = 10 m/s. KE = 1/2 * m * v^2 = 1/2 * 1000 kg * (10 m/s)^2 = 50000 J.

Correct Answer: C — 2000 J

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Q. If a 2 kg object is lifted to a height of 5 m, what is the work done against gravity? (g = 10 m/s²) (2019)

A. 20 J
B. 10 J
C. 50 J
D. 30 J

Solution

Work Done = mgh = 2 kg * 10 m/s² * 5 m = 100 J

Correct Answer: A — 20 J

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Q. If a 5 kg object is dropped from a height of 20 m, what is its potential energy at the top? (2021)

A. 100 J
B. 200 J
C. 50 J
D. 150 J

Solution

Potential Energy (PE) = m * g * h = 5 kg * 9.8 m/s^2 * 20 m = 980 J (approx. 1000 J)

Correct Answer: B — 200 J

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Q. If a force of 10 N moves an object 5 m in the direction of the force, what is the work done? (2020)

A. 50 J
B. 10 J
C. 5 J
D. 25 J

Solution

Work Done (W) = Force (F) * Distance (d) = 10 N * 5 m = 50 J

Correct Answer: A — 50 J

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Q. If a force of 15 N is applied to move an object 3 m, what is the work done? (2023)

A. 45 J
B. 30 J
C. 60 J
D. 15 J

Solution

Work Done (W) = Force * Distance = 15 N * 3 m = 45 J

Correct Answer: A — 45 J

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Q. If a machine does 200 J of work in 10 seconds, what is its power? (2022)

A. 20 W
B. 10 W
C. 30 W
D. 40 W

Solution

Power (P) = Work / Time = 200 J / 10 s = 20 W

Correct Answer: A — 20 W

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Q. If a machine does 200 J of work in 5 seconds, what is its power? (2022)

A. 40 W
B. 50 W
C. 20 W
D. 30 W

Solution

Power (P) = Work Done (W) / Time (t) = 200 J / 5 s = 40 W

Correct Answer: B — 50 W

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Q. If a machine does 2000 J of work in 5 seconds, what is its power? (2022)

A. 400 W
B. 200 W
C. 100 W
D. 500 W

Solution

Power (P) = Work Done / Time = 2000 J / 5 s = 400 W

Correct Answer: A — 400 W

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Q. What is the work done when a force of 15 N moves an object 3 m in the direction of the force? (2021)

A. 45 J
B. 30 J
C. 15 J
D. 60 J

Solution

Work Done (W) = Force * Distance = 15 N * 3 m = 45 J.

Correct Answer: A — 45 J

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Mechanics - Work, Energy & Power

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