Basic electrotechnical units and theory
89
Example 2
A hydroelectric power station pump motor working continuously during period raises
856tonnes water through vertical distance 60m.81kW.81m/s2
. Every
time open door, turn tap tighten nut with spanner, we
exert lever-action turning force.
Levers and turning force
Definition
A lever allows heavy load lifted
or moved small effort.
Load force Distance from fulcrum
Effort force Distance from fulcrum
This formula can perhaps better understood referring Fig. The mechanical advantage of
a simple lever dependent upon the length lever either side the
fulcrum.
A lever allows heavy load lifted moved small effort. Determine the rating (power) the
motor, assuming the acceleration due gravity 9.
Power
Mass Acceleration Distance moved
Time taken
W
)
but Velocity
Distance
Time
(m/s)
Power Mass Acceleration Velocity
Power m/s m/
500 2
2
.2.81m/s2
. lever any rigid body which pivots
or rotates about fixed axis fulcrum.
From Example 1,
Power
Mass Acceleration Distance moved
Time taken
W
Power
( )
85
56 1000 60
7 60
20 000
2
kg m/s m
s
Power W
. this way the crowbar said provide ‘mechani-
cal advantage’. A
small effort long distance from the fulcrum can balance large load. s
s
Power W. washbasin tap and spanner both provide mechanical
advantage through the simple lever action. Applying the principle turning forces lever, obtain the
formula:
Definition
A lever any rigid body which piv-
ots rotates about fixed axis or
fulcrum. Calculate the rating
(power) the motor the acceleration due gravity 9. 4.
,
The rating the pump motor 20kW.
9810
The rating the hoist motor 9.
Example 3
An electric hoist motor raises load 500kg velocity 2m/s. The simplest form lever the
crowbar, which useful because enables person lift load one
end which greater than the effort applied through his her arm mus-
cles the other end
