2. A locomotive drawing a train exerts a draw bar pull of 11,000 lbs. How much work does it do in moving 3 miles? What is its _rate_ of work if it moves 3 miles in 5 minutes? Express in horse-power.[G] [G] The following formula is of assistance in computing _horse-power_ in problems: H. p. = (lbs. × ft.)/(550 × sec.). 3. If 400 kg. are lifted 35 meters in 5 seconds what work is done? What is the rate of work? Express in horse-power, watts and kilowatts. 4. Trace the energy of a moving railway train back to its source in the sun. 5. Why does turning the propeller of a motor boat cause the boat to move? 6. Does it require more power to go up a flight of stairs in 5 seconds than in 10 seconds? Explain. Is more work done in one case than in the other? Why? 7. Can 1 man carrying bricks up to a certain elevation for 120 days do as much work as 120 men carrying up bricks for 1 day? 8. If the 1 man and 120 men of problem 7 do the same amount of work have they the same power? Explain. 9. If 160 cu. ft. of water flow each second over a dam 15ft. high what is the available power? 10. What power must an engine have to fill a tank 11 × 8 × 5 ft. with water 120 ft. above the supply, in 5 minutes? 11. A hod carrier weighing 150 lbs. carries a load of bricks weighing 100 lbs. up a ladder 30 ft. high. How much work does he do? 12. How much work can a 4-horse-power engine do in 5 minutes? 13. Find the horse-power of a windmill that pumps 6 tons of water from a well 90 ft. deep in 30 minutes. 14. How many horse-power are there in a waterfall 20 ft. high over which 500 cu. ft. of water pass in a minute? 15. The Chicago drainage canal has a flow of about 6000 cu. ft. a second. If at the controlling works there is an available fall of 34 ft. how many horse-power can be developed? 16. How long will it take a 10-horse-power pump to fill a tank of 4000 gallons capacity, standing 300 ft. above the pump? 17. A boy weighing 162 lbs. climbs a stairway a vertical height of 14 ft. in 14.6 seconds. How much power does he exert? 18. The same boy does the same work a second time in 4.2 seconds. How much power does he exert this time? What causes the difference? 19. What is a horse-power-hour? a kilowatt-hour? (3) SIMPLE MACHINES AND THE LEVER =116. Machines and Their Uses.=--A man, while standing on the ground, can draw a flag to the top of a pole, by using a rope passing over a pulley. A boy can unscrew a tightly fitting nut that he cannot move with his fingers, by using a wrench. A woman can sew a long seam by using a sewing machine in much less time than by hand. A girl can button her shoes much quicker and easier with a button-hook than with her fingers. These illustrations show some of the reasons why machines are used. In fact it is almost impossible to do any kind of work efficiently without using one or more machines. =117. Advantages of Machines.=--(a) Many machines make possible an _increased speed_ as in a sewing machine or a bicycle.