IN PHYSICS. 211 



53. A body is thrown vertically upward with a velocity 

 of 100 metres. How long before it will return to its 



original position ? 



Ans. 20.4 seconds. 



54. How long will be required for a body to fall a 

 distance of 2,000 metres ? 



Equation (6) d = \gt 2 . 2,000 = - 1\ 

 .*. / = 20.2 seconds. 



55. If two bodies weighing respectively i kilo, and i 

 demi-kilo. are connected by a rod 9 decimetres long, where is 

 the centre of gravity ? 



Ans. 6 dm. from one body and 3 dm. from the other. 



(See Key, p. 10, Question 7.) 



ELEMENTS OF MACHINES. 



79. 1-26. (See Answers on pp. 20 to 24 of this 

 Key.) 



27. Why is the rim of a fly-wheel made so heavy ? 



The heavier the wheel, the greater its inertia ; and the 

 further the weight is from the centre of motion (or axle), 

 the greater its inertia or centrifugal force. 



(See Physics, p. 78.) 



28. Describe the hammer, when used in drawing a nail, 

 as a bent lever, i. e., one in which the bar is not straight. 



If a lever is bent, or if, when it is straight, the bar is 

 not at right angles to the lines of action of the P and 

 the W, it is necessary to distinguish between the arms of 



