NCERT Solutions for Chapter: Work and Energy, Exercise 3: Long Answer Questions

Four men lift a $250 \mathrm{kg}$ box to a height of $1 \mathrm{m}$ and hold it without raising or lowering it. How much work is done by the men in lifting the box? (Take, $g=10 \mathrm{m} {\mathrm{s}}^{-2}$)

Four men lift a $250 \mathrm{kg}$  box to a height of $1 \mathrm{m}$ and hold it without raising or lowering it. How much work do they do in just holding it?

Four men lift a $250 \mathrm{kg}$ box to a height of $1 \mathrm{m}$ and hold it without raising or lowering it. Why do they get tired while holding it?

What is power? How do you differentiate 'kilowatt from kilowatt hour? The Jog Falls in Karnataka state are nearly $20 \mathrm{m}$ high. $2000$ tonnes of water falls from it in a minute. Calculate the equivalent power if all this energy can be utilised? $\left(g=10 \mathrm{m} {\mathrm{s}}^{-2}\right)$

How is the power related to the speed at which a body can be lifted? How many kilograms will a man working at the power of $100 \mathrm{W}$, be able to lift at constant speed of $1 \mathrm{m} {\mathrm{s}}^{-1}$ vertically? .

Define watt. Express kilowatt in terms of joule per second. A $150 \mathrm{kg}$ car engine develops $500 \mathrm{W}$ for each kg. What force does it exert in moving the car at a speed of $20 \mathrm{m} {\mathrm{s}}^{-1}$?

Compare the power at which each of the following is moving upwards against the force of gravity? (given  $g=10 \mathrm{m} {\mathrm{s}}^{-2}$)

$1.$ A butterfly of mass $1.0 \mathrm{g}$ that flies upward at a rate of $0.5 \mathrm{m} {\mathrm{s}}^{-1 }$.

$2.$ A $250 \mathrm{g}$ squirrel climbing up on a tree at a rate of $0.5 \mathrm{m} {\mathrm{s}}^{-1}$.

Compare the power at which each of the following is moving upwards against the force of gravity? (given  $g=10 \mathrm{m} {\mathrm{s}}^{-2}$)

A $250 \mathrm{g}$ squirrel climbing up on a tree at a rate of $0.5 \mathrm{m} {\mathrm{s}}^{-1}.$