274 



PC PASSENGER-BRAKE EQUIPMENT 



by the curve in the accompanying chart, which was plotted 

 from the values given in the third column of the table. Both 

 the table and the curve show that the energy of each 1,000 Ib. of 

 train is four times as great at 20 mi. per hr. as at 10 mi. per hr.; 

 nine times as great at 30 mi. as at 10 mi. ; sixteen times as great 

 at 40 mi.; twenty-five times as great at 50 mi.; thirty-six times 

 as great at 60 mi. ; and forty-nine times as great at 70 mi. In 



I 



8 



$30 



20000 4 e 8 1O 12 14 16OOOO 



Energy in Foot-Pounds per 1OOO Poundf of Train 



other words, at 70 mi. per hr., the brake has to do forty-nine 

 times as much work to stop the train as it would at 10 mi. 

 per hr. 



Suppose that a train weighs 1,650,000 Ib. Then, according 

 to the fourth column of the table, the brake must destroy 

 5,857,500 ft.-lb. of energy in stopping the train at 10 mi. per hr. ; 

 whereas, at 70 mi. per hr., it must destroy 287,017,500 ft.-lb. of 

 energy, an amount sufficient to raise the entire train 174 ft. 



