MACHINES 193 



9. How far must the rope be pulled to lift the weight three feet? 



10. How much force is needed to move a 200-pound load up an incline 

 1000 feet long and 50 feet high? 



11. A man lifts a box weighing 100 pounds into a doorway 3 feet high. 

 How much power would he have needed to move the box up an inclined 

 board 6 feet long? 



12. How much force would have been required if the board mentioned 

 in question 11, were twelve feet long? 



13. How much will a jack-screw lift if it has a pitch of % inch and is 

 operated by a bar two feet long to which a force of 100 pounds is applied? 



14. Opposite the names in the following list write the name of the 

 machine it represents : a chisel, an axe, a grindstone, a propeller, a wheel- 

 barrow, an electric fan. 



15. Why may the pressure of pushing a cork into a large bottle cause 

 it to break? 



ia 



