© 2026 LearnInShort
Tired Is Not the Same as Work
Ask a student what "work" means and you get the everyday answer: effort, sweat, tiredness. Physics does not accept that answer, and every year some paper cashes in on the difference. A man standing all day holding a 40 kg suitcase is exhausted — and has done exactly zero work on the suitcase, because the suitcase never moved.
Work in physics needs two things together: a force, and a displacement along that force. Remove either one and the work is zero, however hard it felt.
Energy is simply the capacity to do that work, and power says how fast you spend it. Three definitions and four formulas carry the entire chapter. In general-science sections this block is worth one or two safe marks — and they stay safe only if you answer from the definition instead of from intuition.
1. A coolie carries a suitcase on his head and walks 50 m along a level platform. The work done by him against gravity is:
2. One horsepower is equal to approximately:
3. If the speed of a moving body is made three times, its kinetic energy becomes:
4. One kilowatt-hour is equal to:
5. A ball of mass 500 g moving at 4 m/s is brought to rest by a fielder. The work done by the fielder's hands on the ball is:
6. A 2 kg stone is dropped from a height of 20 m. Taking g = 10 m/s², its kinetic energy just before hitting the ground is:
7. A machine does 6000 joules of work in 30 seconds. Its power is:
8. Which one of the following is NOT a unit of energy?