Question

A man weighing 600N carries a load of 150N up the stairs $6m$ high in $15 seconds$. His power will be:
A) $290W$
B) $350W$
C) $300W$
D) $200W$

Answer 1

Hint: Recall that when a body moves from its position to some other position then some work is to be done in order to displace it. This work done is defined as the product of the component of force and the magnitude of the displacement. The S.I. unit of work is joule.

Complete step by step solution:
Work done is given by the formula
$W = \overrightarrow F .\overrightarrow s $
Where ‘F’ is the force
And ‘s’ is the displacement
The total force that a man weighs is $ = 600 + 150N$
Or it can be written that $F = 750N$
The height of stairs or the distance that the man has to cover is $s = 6m$
Substituting the given values in the above formula
$W = 750 \times 6$
$W = 4500J$
The power is defined as the rate at which the energy is transferred or the work is done.
The power is given by the formula
$P = \dfrac{W}{t}$
Where ‘W’ is the work done
And ‘t’ is the time taken and the given time is $ = 15\sec $
Substituting the given values and solving for power, we get
$\Rightarrow P = \dfrac{{4500}}{{15}}$
$\Rightarrow P = 300W$
The power of the man will be $300W$.

Option C is the right answer.

Note: It is important to remember that power does not have any direction. So it is a scalar quantity. It's S.I. The unit is Watt. Watt is defined as the amount of power that is required to do one joule of work in one second. Whereas one joule is defined as the work done by a force of 1N to move an object to a distance of 1 meter in the direction of force applied.