FALLING BODIES. 67 



EXERCISES. 



1. What will be the velocity of a body after it has fallen 4 

 seconds ? 



Solution : v = gt. 



v = 32.16x4. 



v = 128.64. Ans. 128.64 ft. 



i 



2. A body falls for several seconds ; during one it passes over 

 530.64 feet ; which one is it? 



Solution : s = \g (2t - 1). 



530.64 = 16.08 x (2t - 1). 



33 = 2t - 1. 



34 = 2t. 



17 = t. Ans. 17th second. 



3. A body was projected vertically upward with a velocity = 96.48 

 feet ; how high did it rise ? 



Solution : v = gt. (See 132.) 



96.48 = 32.16*. 

 3 = t. 

 S=\gt\ 

 8 = 16.08 x 9. 

 S = 144.72. Ans. 144.72 ft. 



4. How far will a body fall during the third second of its fall ? 



5. How far will a body fall in 10 seconds ? Ans. 1608 ft. 



6. How far in | second? Ans. 4.02 ft. 



7. How far will a body fall during the first one and a half seconds 

 of its fall ? 



8. How far in 12 1 seconds ? 



9. A body passed over 787.93 feet during its fall ; what was the 

 time required ? Ans. 7 sec. 



10. What velocity did it finally obtain ? 



11. A body fell during 15i seconds ; give its final velocity. 



12. In an Att wood's machine the weights carried by the thread 

 are 6| ounces each. The friction is equivalent to a weight of two 

 ounces. When the " rider," which weighs one ounce, is in position, 

 what will be its gain in velocity per second ? 



13. A stone is thrown horizontally from the top of a tower 

 257.28 ft. high with a velocity of 60 ft. a second. Where will it 

 strike the ground ? 



