Define work,energy,and power. Give the $SI$ units for each of these quantities. $A$ man whose mass is $80 \, kg$ climbs up $30$ steps of the stairs in $30 \, s$. If each step is $12.5 \, cm$ in height,calculate the power used in climbing the stairs. $(g = 10 \, m \, s^{-2})$

(100 W) Work: The work done by a constant force is defined as the product of the force in the direction of the displacement and the magnitude of the displacement. Its $SI$ unit is joule $(J)$.
Energy: The capacity of a body to do work is termed as energy. Its $SI$ unit is joule $(J)$.
Power: Power is defined as the rate of doing work. Its $SI$ unit is watt $(W)$.
Given: Mass $m = 80 \, kg$,number of steps $= 30$,height of each step $= 12.5 \, cm = 0.125 \, m$,time $t = 30 \, s$,acceleration due to gravity $g = 10 \, m \, s^{-2}$.
Total height $h = 30 \times 0.125 \, m = 3.75 \, m$.
Work done $W = mgh = 80 \times 10 \times 3.75 = 3000 \, J$.
Power $P = W / t = 3000 / 30 = 100 \, W$.