u6 ELEMENTARY SCIENCE 



of the lever were four feet from the fulcrum, how much 

 strength would it take to lift the stone by means of the 

 lever? 



4. Explain the pulley. 



5. Explain the difference between levers of the first, second, and 



third classes. 



6. A ton of coal must be raised twelve feet. The force which can 



be applied is one hundred and fifty pounds. What is the 

 shortest inclined plane which can be used for this purpose? 



7. In what class of levers do the following belong: the drawbridge, 



the teeter-totter, the spring-board, the can-opener? 



