IN NATURAL PHILOSOPHY. 13 



31. A stone let fall from a bridge strikes the water in three 

 seconds. What is the height ? 



Equation (2), d = 16t\ d = 16 x 3 9 = 144 feet. 



32. A stone falls from a church steeple in 4 seconds. What 

 is the height? 



Equation (2), d = 16* a . d = 16 x 4 s = 256 feet. 



33. How far would a body fall the first second at a height 

 of 12,000 miles above the earth's surface? 



(16,000 mi.) a : (4000 mi,) 2 : : 16 feet : x = 1 foot. 



34. A body at the surf ace of the earth weighs 100 tons : 

 what would be its weight 1 ,000 miles above ? 



,(5000 mi.) 3 : (4000 mi.) 2 : : 100 tons : x = 64 tons. 



35. A boy wishing to find the height of a steeple lets fly an 

 arrow that just reaches the top and then falls to the ground. 

 It is in the air 6 seconds. Required the height. 



Equation (2), d = 16< a . d = 16 x 3* = 144 ft. 



36. A cat let fall from a balloon reaches the ground in 10 

 seconds. Required the distance. 



Equation (2), d = 16 x 10 a = 1600 ft, 



37. In what time will a pendulum 40 feet long make a 

 vibration f 



According 1o the third law of pendulums, and taking the length of a seconds 

 pendulum as 39 in., we have : 



1 sec. : x : : V9 : 1/40x12 in. 



x = 3.5+ sec. 



In what time will a pendulum 52 feet long make a vi 

 bration? 



