A girl whose mass is 40kg walk up a flight of 20steps each 15mm hight in 10seconds. find power developed by the girl showing the solution ​

Approximately 11.76 joules per second

Work Shown:

Mass = 40 kg

Force pulling down = (mass)*(gravity) = 40*9.8 = 392 newtons

Roughly 392 newtons of force are pulling down on her.  

To climb the steps, she must apply 392 newtons of force upward.  

Displacement = 20*(15 mm) = 300 mm = 0.3 m

Work = Force*Displacement

Work = 392*0.3

Work = 117.6 joules of energy

Power = (Work)/(Time)

Power = (117.6 joules)/(10 seconds)

Power = (117.6/10) joules per second

Power = 11.76 joules per second, which is approximate