v MATTER IN RELATION TO MOTION 71 



strings passing over the edge of a table with two other masses of 

 3 Ibs. and 18 Ibs. respectively. What are their accelerations and which 

 Avill reach the edge of the table first if both are placed at a distance 

 of 12 feet from that edge ? 



39. Two masses of 5 Ibs. and 7 Ibs. are connected by a light string 

 which passes over a smooth pulley. Find their common accelera- 

 tion and the velocity of either after they have been moving for 3 

 seconds. (The student must think here what is the moving force ? 

 and what is the mass on which it acts ?) 



40. A certain force F acting for 10 seconds produces in a mass of 

 17 Ibs. a velocity of 12 feet per second ; another force F', acting for 

 10 minutes, produces in a mass of 17 cwt. a velocity of 12 yards per 

 minute. Find the ratio of F to F'. 



41. One force acting on a mass of 12 Ibs. gives it a velocity of 

 5 feet per second, in one-third of the time that another force acting 

 on a mass of 9 Ibs. takes to give it a velocity of 8 feet per second, 

 Compare the forces. 



42. What force will set up in a mass of 5 Ibs. a velocity of 80 feet 

 per second in 5 seconds ? 



43. How many units of force (foot-pound-second system of units) 

 must act on a mass of 16 Jbs. for 4 seconds so as to give it a velocity 

 of 35 yards per minute ? 



44. *A certain force acting on a mass of 10 Ibs. for 5 seconds, pro- 

 duces in it a velocity of 100 feet per second. Compare the force 

 with the weight of 1 Ib. , and find the acceleration it would produce 

 if it acted on a ton. 



45. Equal forces act for the same time on two bodies A 

 and B, the mass of the first being four times that of the second. 

 What is the relation between the momenta generated by the 

 forces ? 



46. A force moves a body 18 feet in 3 seconds, starting from a 

 position of rest. Find the ratio of the force to the weight of the 

 body. 



47. A pressure equal to the weight of 3 Ibs. acts on a mass of 8 Ibs. 

 starting from rest. Find the distance over which the mass will 

 move in 4 seconds. 



48. A horizontal force which would statically support 5 Ibs., 

 acted continuously for 3 seconds on a heavy body initially at rest on 

 a smooth horizontal plane, and at the end of that time the body 

 was moving with a velocity of 200 yards per minute. Determine 

 (a) the acceleration and (b) the mass of the body. 



49. A mass of 1 2 Ibs. rests on a horizontal table. Find the pressure 

 of the mass upon the table when the table is made to descend with 

 a uniform acceleration of 5 feet per second per second. 



50. A man whose weight is 160 Ibs. is standing in a lift. What 

 pressure will he cause on the bottom of the lift when it is (a) ascend- 

 ing, (b) descending with uniform acceleration \g'>. 



51. Ten pounds hangs by a string from a point which ascends 

 with an acceleration of 2 (feet per second per second) ; find the 

 tension of the string. 



52. A bullet, weight 1 oz. , is fired from a rifle ; if it has a velocity 



