Question

A body does 75 J of work in 10 second. What is its power?

Answer 1

Hint: The work done by the body and the time taken are given, these values can be substituted in the formula of power to calculate the value of the same.

Formula Used:
$P = \dfrac{W}{T}$ where,
P = Power
W = Work done
T = Time taken

Complete step by step answer:
Definitions of the respective terms:
Work: When an object gets displaced from its position by an application of external force, the work is said to be done. It is given as:
Work = Force $\times$ Displacement
\[W = F \times D\]
Power: Power is defined as the rate of work done on an object. It is the work done per unit time and is given as:
Power = $\dfrac{{Work}}{{Time}}$
$P = \dfrac{W}{T}$ __________ (1)
Now, it is given in the question that:
Work done (W) = 75 J
Time (T) = 10 s
Substituting the values in eqn (1) to calculate the power, we get:
$P = \dfrac{{75}}{{10}}$
P = 7.5
The SI unit of power is watt (W)
P = 7.5 W
Therefore, the power of a body that does 75 J of work in 10 seconds is 7.5 watt

Note:When we talk about the rate of a quantity, it is its value with respect to time and can also be written in the derivative form. E.g. rate of quantity A can be given as:
$\dfrac{A}{t}$ or $\dfrac{{dA}}{{dt}}$
SI Units to remember:
Work = Joules (J); units of energy are also the same.
Time = seconds (s)
Power = Watt (W)
If the given values are not in these units, then we are required to carry out the respective conversions.