in TIME, VELOCITY AND ACCELERATION 43 



inches per second per second ; calculate its velocity after it has 

 moved over 20 feet. 



17. Explain the following statements : A body has a velocity 

 whose measure is 30 ; another body an acceleration whose measure 

 is 2 ; in each case with foot second units. If allowed to move freely, 

 how far would the first body travel in half a minute, and in what 

 time would the second body, starting from rest, acquire a velocity 

 of 15 miles an hour ? 



18. A particle which started from rest and was uniformly 

 accelerated, had a velocity of 20 feet per second when it had 

 described 60 feet in a straight line. What was its acceleration and 

 how long had it been in motion ? 



19. Two bodies, whose velocities are accelerated in every second 

 by 3 and 5 feet a second respectively, begin to move towards each 

 other at the same instant, at first they are a mile apart ; after how 

 many seconds will they meet ? 



20. A man runs uniformly round a circular track at the rate of 12 

 miles an hour ; if he pass the same point four times in 5 minutes, 

 what is the length of the track ? 



21. Two stations on a railway are 35 miles apart. A train starts 

 from the first and travels uniformly at the rate of 40 miles per hour 

 towards the second ; another train starts simultaneously from the 

 second station and travels at the rate of 30 miles per hour in the 

 opposite direction. At what time after starting will they meet and 

 at what distance from the two stations respectively ? 



22. A man walking at the rate of 4 miles an hour along a railway 

 line meets a train, 88 yards long, travelling at the rate of 26 mile's 

 an hour. How many seconds elapse while the train is passing 

 him ? 



23. A line is drawn upon the floor of a railway carriage from door 

 to door. When the carriage is at rest a ball is dropped from the 

 roof and falls upon this line. What difference would be 

 observed : 



(a) If the train is moving when the ball is dropped, 

 (ft) If the train starts when the ball is half way down. 

 (c) If the ball is dropped when the train is in motion, but the 

 train stops suddenly when it is half way down ? 



