42 ELEMENTARY GENERAL SCIENCE CHAP. 



The Unit of Acceleration is an increase of unit velocity in a unit 

 of time. It is generally taken as equal to an increase of velocity of 

 one foot per second per second. 



The change of velocity v in t seconds in a body moving from rest 

 with an acceleration of a units is equal to at feet per second. If a 

 uniform acceleration is applied to a body already moving with a 

 uniform velocity 11, then v u + at. 



Other Important Formulae. 



QUESTIONS ON CHAPTER III. 



1. Give a definition of velocity, and state how uniform linear 

 velocity is measured. 



2. What is the difference between a solar day and a mean solar 

 day? 



3. Define a sidereal day and explain how it differs from a solar 

 day. 



4. What is the common unit of time ? How is it related to the 

 period of the earth's rotation ? 



5. Give a brief description of some mechanism in common use for 

 measuring time. 



6. What is the difference between uniform and variable velocities ? 

 How are uniform linear velocities measured ? 



7. Explain how the average velocity of a body moving with a 

 variable velocity is estimated. 



8. The radius of a circle is half a mile ; a horse runs round the 

 circumference at the rate of five miles an hour? what is his velocity 

 in feet per second ? (The result should be carried to the second 

 decimal place.) 



9. Define acceleration and give an example of a body moving with 

 an accelerated velocity. 



10. How is uniform acceleration measured ? Explain the differ- 

 ence between a positive and negative acceleration, giving an example 

 of each. 



11. What is the unit of acceleration? A body moves from rest 

 with a uniform acceleration of 15 feet per second per second ; 

 what is its velocity after 12 seconds ? 



12. The velocity of a body moving from rest has been uniformly 

 accelerated ; if its velocity after 7 seconds be 343 feet per second 

 what has been its acceleration ? 



13. A train starting out of a station is made to move with a 

 uniform acceleration of 25 kilometres per hour per hour ; what is its 

 velocity in kilometres per hour after it has gone a distance of 

 16 kilometres? 



14. How far will a ball go from rest in three seconds if in every 

 second it increases its velocity by a velocity of 9 feet per second ? 



15. A train which is uniformly accelerated starts from rest, and 

 at the end of 3 seconds has a velocity with which it would travel 

 through 1 mile in the next 5 minutes ; find the acceleration. 



16. A body moves from rest with a uniform acceleration of 100 



