LBVEBS 491

the bob on a steelyard, if, at a distance of 12 inches from the fulcrum,
it balances a weight of 20 Ibs. at a distance of 3| inches from it?

Arm x power = arm X weight
12 X P = 3| X 20

P ^ __ ___ vx _ -y______ f>

5 1 12

The bob weighs 6 Ibs.

In levers of the second class the weight is between the fulcrum and the
power (Figure 6).

Example—Find the power exerted by a man pulling upwards on
the end of a lever 10 feet long, the other end of the lever is resting on
the ground, 3 feet under and beyond the corner of a box, which weighs
500 Ibs.

Second Class.

Arm X power=armx weight, but half the weight of the box, 250 lbs.f
is supported on the ground so the man has to lever up 250 Ibs. only.
10 ft, X P = 3 ft. x 250 Ibs.
P = 75 Ibs.
The man exerts a power of 75 Ibs. to tilt the 500 Ibs. box.
Example.—An oar 12 feet long rests in a rowlock 4 feet from the
loom. Two rowers pull with a power of 100 Ibs. each as measured by a
spring balance. Required the propelling pressure or weight acting at
the rowloefc.