PHYSICS. 



209 



46. A ball is dropped from a height of 64 feet. At the 

 same moment a second ball is thrown upward with sufficient 

 velocity to reach the same point. Where will the two balls 

 pass each other ? 



At the end of one second. The first ball would fall 

 64 feet in 2 seconds ; the second would rise for 2 sec- 

 onds, and they would pass in i sec. 



47. Two bodies are successively dropped from the same 

 point with an interval of \ of a second. When will the 

 distance between them be one metre ? 



Let / = time of descent of 2d body. 

 Then /-f .2 = time of descent of ist body. 



Since the space passed over equals 4.9 m. (16 ft.) mul- 

 tiplied by the square of the time, we have 



4.9 / 2 = space passed over by 2d body. 

 4 . 9 (/ + -2) 2 = 4-9' 2 + 1-96' + .196 



= space passed over by ist body. 



The difference between the 2 spaces being i m., we 



have 



4.9/2 + i.96/ + .196 4.9/2 = i m. 



i.96/ = .804. 



/ = .4102 sec. = time of descent of 2d body. 

 .6102 sec. = time of descent of ist body. 



Therefore they will be i m. apart when the ist body has 

 fallen for .6102 sec., or the 2d body for .4102 sec. 



PROOF. 4.9 x .6io2 2 4.9 x .4io2 2 i (nearly). 



WM. H. TAYLOR. 



48. Explain the following fact : A straight stick loaded 

 with lead at one end, can be more easily balanced vertically 



