Question

Convert 28.8 khJ into watt hour.
A. $8\times {{10}^{-3}}$kWh
B. 8 kWh
C. $8\times {{10}^{3}}$ kWh
D. None of these

Answer 1

Energy, as most physical quantities can be represented and measured in many different units. As all these representations represent the same quantity interconverted to one another. The conversion rate of Joule to Watt Hour is given below
Formula Used:
$1Wh=3600J$
$1Wh={{10}^{-3}}kWh$

Complete answer:
Energy, as most physical quantities, can be represented and measured in many different units. As all these representations represent the same quantity interconverted to one another. Two of the most used units of energy are watt-hour and Joule. To convert one unit to another we should know the conversion rate.
Coming to the question we have to convert kilojoules to kilowatt-hours. We know that
$1Wh=3600J$
For using this conversion, we need the energy in Joules.
$28.8khJ=28.8\times {{10}^{3}}J$
And we also know that
$1Wh={{10}^{-3}}kWh$
So putting all these together. The energy in kilowatt-hour would be
$E=\dfrac{28.8\times {{10}^{3}}}{3.6\times {{10}^{6}}}$
$\Rightarrow E=8\times {{10}^{-3}}kWh$
So, the energy in watt-hour would be $8\times {{10}^{-3}}kWh$

Therefore, Option A is the correct one.

Note:
The SI unit of energy is Joule and is written as J. This unit was named in honour of James Prescott Joule. Joule is also the standard unit of Work Done and can be defined as the work done by a force of magnitude 1N acting through a meter of 1 meter. 1 Joule is equal to ${{10}^{7}}$ergs which is a unit used to measure a small amount of work done.