ix WORK AND ENERGY 131 



QUESTIONS ON CHAPTER IX. 



1. In the case of a shot fired at a target, state (a) why the velocity 

 of the shot changes ; and (6) why the target is made hot where the 

 shot strikes it. 



2. Define work, and describe an experiment to prove that a falling 

 ball is capable of doing work. 



3. Explain the terms power of an agent and horse-power. 



4. What is meant by a foot-pound of work ? W T hat is the value of 

 a horse-power in terms of this unit ? 



5. How is kinetic energy measured ? If we wish to express the 

 result in foot-pounds, how do we proceed ? 



6. A man weighing 140 Ibs. puts a load of 100 Ibs. on his back and 

 carries it up a ladder to a height of 50 feet. How many foot-pounds 

 of work does he do altogether and what part of his work is done 

 usefully ? 



7. A body weighing 10 Ibs. is placed on a horizontal plane and is 

 made to slide over a distance of 50 feet by a force of 4 Ibs. What 

 number of units of work is done by the force ? 



8. If a man can work at the rate of 210,000 foot-pounds an hour, 

 how long would it take him to raise a weight of 10 tons through 150 

 feet, supposing him to be provided with a suitable machine ? 



9. A horse pulling a horizontal trace with a force equal to the 

 weight of 72 Ibs., draws a cart along a level road at the rate of 3| 

 miles per hour. What amount of work is done by the horse in 5 

 minutes ? 



10. If a force equal to the weight of 10 Ibs. revolve three times 

 tangentially round a circle of 5 feet radius, find the work it 

 would do. 



11. A cannon-ball whose mass is 60 Ibs. falls through a vertical 

 height of 400 feet. What is its energy at the end of its fall ? 



12. What is the kinetic energy of a mass of 5 Ibs. moving with a 

 velocity of 10 feet per second ? State clearly what the unit is in 

 terms of which your answer is expressed. 



13. A body whose mass is 10 Ibs. is carried up to the top of a 

 house 30 feet high. By how many foot-pounds has the change of 

 position increased its potential energy ? If it is allowed to fall, 

 what number of foot-pounds of kinetic energy will it have when 

 it reaches the ground ? 



14. A particle moving from rest is acted on through 250 feet by a 

 force of 9 pounds. Find its kinetic energy ; and its mass being 

 5 Ibs., find its velocity. 



15. What is the difference between kinetic energy and potential 

 energy ? 



16. Describe an experiment to prove that energy due to visible 

 motion can be transferred from one body to another. 



17. What proof can you adduce that the energy of visible motion 

 can be transformed into heat ? 



18. How do you account for the fact that heat generally appears 

 when motion is lost ? 



K 2 



