192 



EXPERIMENTAL GENERAL SCIENCE 



Practical Exercises 



1. If a weight of 25 pounds be placed on one arm of a lever 10 inches 

 long, how far from the fulcrum must a 10-pound weight be placed on the 

 other arm to exactly balance it? 



2. A meter stick has a fulcrum placed under it, exactly 20 centimeters 

 from one end. On this end a weight of 100 grams is placed. How 

 many grams must be placed on the other end to balance 

 it? 



\ 



p if 5 



3. Two boys make a see-saw of a long plank. If one 

 boy, who weighs 70 pounds, sits eight feet from the fulcrum , 

 at what distance must the other boy, who weighs 56 

 pounds, sit to exactly balance the see-saw? 



4. A man wishes to lift a stone by bearing down with 

 his whole weight on a crowbar 4 feet long. How much can 

 he lift if he weighs 150 pounds and the fulcrum of his lever 

 is three inches from the end of the bar? 



6. Write opposite the following names the class of lever 

 to which each belongs: a pair of scissors, a pump, a wheel- 

 barrow, a pair of tweezers, a bellows, a spade, a door, a 

 nut-cracker, a clawhammer. 



6. A windlass with a crank 2 feet long is used to lift ore 



ou * ^ a mme - K an en? rt of 50 pounds is applied to the 

 crank, how much ore can be lifted at a time if the lifting 

 rope winds up on an axle 6 inches in diameter? 



7. A bucket of water weighing 72 pounds is to be lifted by a windlass 

 with an axle 6 inches in diameter and a crank 18 inches long? How 

 much force must be applied continually to the crank to do the work? 



8. Study the accompanying illustration and decide how many pounds 

 pull on the rope will lift a 100-pound weight? 



