Average Power Over Time
A weightlifter raises a barbell of mass 80 kg from the floor to a height of 2 m above the floor in 4 seconds at a steady rate. Taking g as 10 m/s squared, what is the average power developed by the weightlifter?
Select the correct option:
Solution
400 W
As stated in NCERT Class 11, Chapter 6 (Work, Energy and Power), average power is the total work done divided by the time taken. The work done in lifting the barbell against gravity is W = mgh = 80 × 10 × 2 = 1600 J. Dividing by the time of 4 seconds gives average power P = 1600 / 4 = 400 W. Because the lift is steady, the barbell's kinetic energy does not change, so all the work goes into potential energy. The option 1600 W reports the total work rather than the power. The option 200 W divides by an incorrect time of 8 seconds. The option 640 W misuses the mass and height factors. A unit check confirms joules per second equals watts, and 400 W of sustained mechanical output for a heavy lift over four seconds is physically reasonable for an athlete.
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About This Question
- Subject
- physics
- Chapter
- work, energy and power
- Topic
- average power over time
- Difficulty
- Medium
- Year
- 2025
Solution
Correct Answer:
400 W
As stated in NCERT Class 11, Chapter 6 (Work, Energy and Power), average power is the total work done divided by the time taken. The work done in lifting the barbell against gravity is W = mgh = 80 × 10 × 2 = 1600 J. Dividing by the time of 4 seconds gives average power P = 1600 / 4 = 400 W. Because the lift is steady, the barbell's kinetic energy does not change, so all the work goes into potential energy. The option 1600 W reports the total work rather than the power. The option 200 W divides by an incorrect time of 8 seconds. The option 640 W misuses the mass and height factors. A unit check confirms joules per second equals watts, and 400 W of sustained mechanical output for a heavy lift over four seconds is physically reasonable for an athlete.
This medium difficulty physics question is from the chapter work, energy and power, covering the topic of average power over time. It appeared in the 2025 exam.
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