Question

A machine does $1920$ joule of work in $240\,s$ . What is the power of the machine?

Answer 1

Hint Power is the certain amount of energy to do some work in a certain time. Write the formula of the power in relation to the work done and the time taken, and substitute the known parameters in it to find the value of the power to do that work.
Useful formula:
The formula of the power is given by
$P = \dfrac{w}{t}$
Where $P$ is the power of the machine, $w$ is the work done by the machine and $t$ is the time taken for the machine.

Complete step by step answer
It is given that the
Work done by the machine, $w = 1920\,J$
Time taken for the work done, $t = 240\,s$
Let us use the formula of the power of the machine,
$P = \dfrac{w}{t}$
Substitute the value of the work done and the time taken in the above formula, we get
$P = \dfrac{{1920}}{{240}}$
By doing division in the right hand side of the equation, we get
$P = 8\,W$

Hence the power of the machine consumed for the given work is obtained as $8\,W$ .

Additional information
If the machine has no losses in it, then its input power must be equal to its output power. Then the efficiency of the machine becomes $100\%$ . Since this condition is practically not valid, the efficiency of all the machines must be less than $1$ .

Note Remember that the Watt is the standard system of unit of power. It is obtained by dividing the joule by the time taken. Power is said as the kilowatt hour in practical applications like home power consumption. $1\,$ Joule when converted into kilowatt hour its value becomes $3.6 \times {10^{ - 6}}$ .