Power

P = W/t    

Power is measured in Watts (W) or J/s.We can say that 1 J/s = 1 W. 

Another term which refers to a larger unit of power is horsepower (hp); 1 hp = 746 W.  

Example:  A 70 kg jogger runs up a long flight of stairs in 4.0 s.  The vertical height of the stairs is 4.5m.  What is the jogger’s power output in watts and in horsepower.          

P = W/t  (Work to overcome gravity W = mgh)         P = mgh/t        
P = (70 kg)(9.8 m/s2)(4.5 m)/4.0 s        
P = 770 W  

Since there are 746 Watts in a horsepower, the jogger generates just over one hp.   When the power formula is manipulated to solve for work   W = Pt   we get units of Joules or Watt seconds (Ws) which can be converted into either Joules or another common term for energy - kilowatt hours (kWh).                                     1 kWh = 3 600 000 J                                             = 3.6 x 10⁶ J   OR                                   1 Joule = 1/(3.6 x 10⁶ J)                                             = 2.0 x 10^-7 kWh