Rate of Doing Work: Power

What is the SI unit of power?

Two persons do the same amount of work in $10 \mathrm{s}$ and $20 \mathrm{s}$, respectively. What is the ratio of the power used by the first person to that by the second person?

What do you mean by power of an agent? Give an expression for power.

How many joules are there in one kilowatt hour ($1 \mathrm{kW} \mathrm{h}$)?

What is the power of a body which is doing work at the rate of one joule per second?

Define the term ‘Watt’.

Name two units of power bigger than watt.

Two girls A and B each of weight $400 \mathrm{N}$, climb up a tree of a height of $8 \mathrm{m}$. Girl A takes $20 \mathrm{s}$ while B takes $50 \mathrm{s}$ to accomplish this task. What is the power expended by each girl?

The work done by the heart is $1 \mathrm{J}$ per beat. Find the power of the heart if it beats $72$ times per minute.

A man of mass $60 \mathrm{kg}$ climbs stairs of total length $20 \mathrm{m}$ in $2 \mathrm{minutes}$. Find the power delivered by the man. ($g = 10 \mathrm{m}/{\mathrm{s}}^2$)

An electric bulb consumes $7.2 \mathrm{kJ}$ of electrical energy in $2 \mathrm{minutes}$. What is the power of the electric bulb?

If an electric bulb of $100 \mathrm{W}$ is lighted for $5 \mathrm{hours}$, how much units of energy would be consumed?

The engine of a train has to apply a force of $5000 \mathrm{N}$ to overcome friction to run at a uniform rate of $90 \mathrm{km}/\mathrm{h}$. What is the power developed by the engine?

Determine the power of an engine required to lift $100000 \mathrm{kg}$ of coal per hour from a mine which is $360 \mathrm{m}$ deep. ($\mathrm{g} = 10 \mathrm{m}/{\mathrm{s}}^2$)

An old man does $200 \mathrm{J}$ of work in $10 \mathrm{s}$ and a young man does $100 \mathrm{J}$ of work in $4 \mathrm{s}$. (i) Who is delivering more power? (ii) Find the ratio of the power delivered by the old man to that delivered by the young man.

A boy of mass $40 \mathrm{kg}$ climbs up stairs of $50$ steps, each of $10 \mathrm{cm}$ high, in $5 \mathrm{s}$. Find the power developed by the boy. ($g = 10 \mathrm{m}/{\mathrm{s}}^2$)

A body weighing $10 \mathrm{kg}$ is lifted to a height of $50 \mathrm{m}$ in $20 \mathrm{seconds}$. What is his power? ($g = 9.8 \mathrm{m}/{\mathrm{s}}^2$)

An object does $20 \mathrm{J}$ of work in $5$ seconds. What is its power?