280 APPLIED MECHANICS 
120 Ibs. per square inch. What horse-power will be absorbed by the friction of 
this pivot when running at 200 revolutions per minute with a coefficient of 
friction equal to 0:005 ? 
17. The thrust shaft of a marine engine indicating 4500 horse-power has 8 
collars 26} inches diameter, the diameter of the shaft between the collars being 
16? inches. Taking the coefficient of friction at 0°04, the intensity of the thrust 
pressure at 50 lbs. per square inch, and the speed of the shaft 80 revolutions 
per minute, what horse-power is absorbed by friction in the thrust bearing, and 
what percentage is it of the horse-power of the engine? 
18. A straight lever mounted on an axle 2 inches in diameter has arms 
5 inches and 10 inches long, measured from the centre of the axle. There is a 
load W of 100 lbs. at the end of the short arm, and a vertical force P at the end 
ofthelong arm, Tak- 
ing the coefficient of 
friction »=0'1, find P, 
(1) to just raise W, 
(2) to just lower W. 
19. A weight W of 
500 lbs. hangs by a W 
rope which is coiled 
phrase: Mache Saag paet Fra. 437. Fig. 438. Fra. 439. 
effective diameter is 
12 inches. The barrel is fixed on an axle whose diameter is 3 inches. W may 
be raised or lowered by a vertical force P acting at the circumference of a wheel 
30 inches in diameter, also fixed to the axle. Find P to raise W with a uniform 
velocity, («) when P acts as shown in Fig. 438, (b) when P acts as shown in 
Fig. 439. Also find P to lower W with a uniform velocity in each case. 
p=O01. 
20. Referring to Fig. 413, p. 270. a=30 inches, b2=10 inches, r=1°5 inches, 
6=60°, angle CBO=angle CAO=90°, sing=0'1, and Q=600 Ibs. Find P (a) to 
just raise Q, (b) to just lower Q. 
21. Fig. 440 shows a bent lever AOB. The fulcrum at O is in a loose cylindric 
bearing 4 inches diameter. AO is 12 inches, : 
BO is 24 inches; the force Q of 1000 lbs. acts 
at A. What force P acting at B will just 
overcome Q, (1) when friction is neglected, 
(2) when the coefficient of friction is 0°3. Find 
also the line of action and magnitude of the Fic. 440 
force R acting on the lever at O. [B.E.] 2 
22. A crank disc (Fig. 441) receives an oscillating motion through an angle 
AOB by a “gab” ended rod CD driven 
by an eccentric. At (a) the crank pin is 
shown below, and at (b) above the centre 
of the disc. Show that in one of these 
arrangements the effect of the friction 
between the pin and the “ gab,” during 
both the forward and return strokes, will 
be to throw the “ gab” off the pin, while 
in the other the effect will be to keep the 
sé gab ” on the pin. Fia. 441, , 
23. An ordinary horizontal direct acting steam-engine mechanism is shown 
in a particular position in Fig. 442, AB being the connecting-rod, and BC the 
crank. The diameters of 
the journals at A, B, and 
C are 5, 8, and 74 inches 
respectively. The force P 
transmitted through the 
piston-rod to the cross- 
head is 6000 lbs. Q, the 
useful resistance to the 
motion of the crank shaft, Fra. -442, 
acts in a vertical direction 
at a perpendicular distance of 12 inches from the axis of the shaft, as shown. 
