6 7 



spring balance and draw the roller uniformly upward 

 along the plank as shown in the figure. Note carefully 

 the pull registered on the spring balance. 



Weigh the roller, and compare its real weight with the 

 force indicated by the spring balance as necessary to raise 

 it along the incline. 



If work equals force x distance, how many foot pounds 

 of work would be expended in lifting the roller directly 

 from A to B ? 



How much work is done in pulling the roller along the 

 plank in an effort to raise it to A ? 



Is there any advantage in the use of the plank ? 



Is there any disadvantage in the use of 

 the plank ? 



Is it, on the whole, advantageous or 

 not? Illustrate. 



EXPERIMENT 57. 

 LEYS 



PTJL- 



W 



A pulley is a grooved 

 wheel around which a 

 cord passes. 



(a) Fasten a pulley 

 to a support as shown 

 in Figure 55. What 

 weight at P will bal- 

 ance 20 pounds at W1 

 Is there any advan- 

 tage to be obtained 

 from the use of this 

 FIG. 55. A fixed pulley, type of pulley ? 



FIG. 56. A movable 

 pulley. 



