2.
9810
The rating the hoist motor 9.81m/s2
.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.
,
The rating the pump motor 20kW. Applying the principle turning forces lever, obtain the
formula:
Definition
A lever any rigid body which piv-
ots rotates about fixed axis or
fulcrum. 4. this way the crowbar said provide ‘mechani-
cal advantage’.
Load force Distance from fulcrum
Effort force Distance from fulcrum
This formula can perhaps better understood referring Fig. Every
time open door, turn tap tighten nut with spanner, we
exert lever-action turning force. s
s
Power W.
Example 3
An electric hoist motor raises load 500kg velocity 2m/s.
A lever allows heavy load lifted moved small effort. 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.81m/s2
. washbasin tap and spanner both provide mechanical
advantage through the simple lever action. A
small effort long distance from the fulcrum can balance large load. lever any rigid body which pivots
or rotates about fixed axis fulcrum. Determine the rating (power) the
motor, assuming the acceleration due gravity 9.
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
.81kW.
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
. Calculate the rating
(power) the motor the acceleration due gravity 9. The mechanical advantage of
a simple lever dependent upon the length lever either side the
fulcrum.
Levers and turning force
Definition
A lever allows heavy load lifted
or moved small effort
