physics
posted by sarsi on .
A labour is throwing 12 bricks per min from the ground and these just reach the roof which is 3.3 meters high. ifthe weight of each bricks be 3.75 kg then find the horse power with which the labour is working.

Power is rate of work.
Work is force times displacement.
Force is weight of each brick under gravity. Measure weight in [kgf] (kilogramforce: the weight of 1[kg] in normal gravity).
The conversion rate to metric horsepower is: 1[hp] = 75 [kgf·m/s]
Use: P = Ws/t
Where:
(1/t) = 12[/min] = 0.2[/s]
s = 3.3[m]
W = 3.75[kgf] 
12 bricks/min*(1min/60s)=0.2bricks/s
m=(3.75kg/brick)
F=mg=(3.75kg/brick)*9.8m/s^2=36.75N/brick
d=3.3m
Since Power=Work/t(s)=F*d/t
Power=(36.75N/brick)*(0.2bricks/s)*(3.3m)=24.3 W
***Bricks cancel leaving (N*m)/s
24.3 W*(1hp/745.70 W)=0.0325 hp