Mechanics of engineeringComprising statics and dynamics of solids: and the mechanics of the materials of constructions, or strength and elasticity of beams, columns, arches, shafts, etc . P = mean pressure on one oar-handle ; hence the pressureson the foot-rest are 2P, resistances. Let Jf=massof boatand load, v0 and vn its velocities at beginning and end of = pressures between oar-blade and water. R = mean re-sistance of water to the boats passage at this (mean) are the only (horizontal) forces to be considered as act-ing on the boat and two oars, considered free collecti
Mechanics of engineeringComprising statics and dynamics of solids: and the mechanics of the materials of constructions, or strength and elasticity of beams, columns, arches, shafts, etc . P = mean pressure on one oar-handle ; hence the pressureson the foot-rest are 2P, resistances. Let Jf=massof boatand load, v0 and vn its velocities at beginning and end of = pressures between oar-blade and water. R = mean re-sistance of water to the boats passage at this (mean) are the only (horizontal) forces to be considered as act-ing on the boat and two oars, considered free the stroke the boat describes the space s3 = CD, the-oar-handle the space sa = AB, while the oar-blade slips back- WORK, ENERGY, AND POWER. 161 ward through the small space (the slip) == s1 (average).Hence by eq. (XVI.), § 142, 2Ps, - 2Ps3 -Its, - 2PA = \M{< - <);, 2P(s-s3)=2PxA£=2Ps =Ps3+2PlSl+ iM(vn*-v;); or, in words, the product of the oar-handle pressures into thedistance described by them measured on the boat, , the workdone by these pressures relatively to the boat, is entirely ac-counted for in the work of slip and of liquid-resistance, and in-. Fia 166. creasing the kinetic energy of the mass. (The useless workdue to slip is inevitable in all paddle or screw propulsion, aswell as a certain amount lost in machine-friction, not consideredin the present problem.) During the recover the velocitydecreases again to v0. 155. Examples.—1. What work is done on a level track, inbringing up the velocity of a train weighing 200 tons, fromzero to 30 miles per hour, if the total frictional resistance (atany velocity, say) is 10 lbs. per ton, and if the change of speedis accomplished in a length of 3000 feet % {Foot-ton-second system.) 30 miles per hour = 44 ft. persec. The mass = 200 -f- = ;•\ the change in kinetic energy, (= iMv* -iMx 03),= £() X 442 = 162 MECHANICS OF ENGINEERING. The work done in overcoming friction
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectenginee, bookyear1888
