Question

(i)write the relation between commercial unit of electricity and the SI unit of energy .

(ii) a boy of mass 45 kg climbs up 20 steps in 20 sec. if each step is 25cm high, calculate the power used in climbing.
3 mark question if u answer correctly i will mark u brainliest detailed answer is expected

Answer 1

(i) Commercial Unit of Energy. The SI unit joule is too small to express very large quantities of energy. Hence we use a bigger unit called kilowatt hour (kWh) to express energy. 1 kWh is the amount of energy consumed by an electrical gadget in one hour at the rate of 1000 J/s or 1kW.


(ii) m= 45kg 

Number of steps = 20

Each step = 25cm

Total height climbed = 20*25= 500cm = 5m

Time= 20sec 

According to the formula, 

Power = mgh/time
= 45*9.8*5/20
= 2205/20
= 110.25 W