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?