12 ANSWERS TO PRACTICAL QUESTIONS 



22. What is the proportionate time of vibration of two pen* 

 dulutns^ 1 6 and 64 inches long, respectively ? 



According to the third law of pendulums, 

 Time of vib. of 1st : Time of vib. of 2d : : v/16 : v/64 : : 4 : 8 : : 1 : 2. 



23. Why, when you are standing erect against a wall, and 

 a piece of money is placed between your feet, can you not stoop 

 forward and pick it up ? 



By leaning forward you bring the centre of gravity in front 

 of your feet, and, as on account of the wall, you cannot throw 

 any part of your body back to preserve the balance, you fall 

 forward. 



24. If a tower were 198 feet high, with what velocity would 

 a stone dropped from the summit, strike the ground f 



According to equation (3), t> 2 = 64 d. t? 2 = 64 x 198. 0=112.5 feet. 



25. A body falls in 5 seconds : with what velocity does it 

 strike the ground? 



According to equation (1), v = 32 t. v =32 x 5. v =160 feet. 



26. How far will a body fall in 10 seconds ? 



According to equation (2), d = 16 2 . d = 16 x 10 2 = 1600 feet. 

 With what velocity will it strike the ground? 



According to equation (1), v = 32 t. v = 32 x 10 = 320 feet. 



27. A body is thrown upward with a velocity of 192 feet the 

 first second ; to what height will it rise ? 



Equation (1), v = 32 t. 192 = 32 t. t = Q sec. 



(2), d = 16 P. d = 16 x 6 2 =576 feet. 



28. A ball is shot upward with a velocity of 256 feet ; to 

 what height will it rise ? How long will it contin ue to ascend f 



Using equations (1) and (2), as in the last problem, we hare : 



t = 8 sec. 

 d = 1024 feet. 



30. Are any two plumb-lines parallel? 

 They are not, since they all point to the centre of the earth. 

 No two spokes of a wheel can be parallel 



