72 ELEMENTARY GENERAL SCIENCE CHAP. 



of 1,520 feet per second on leaving the barrel, what will be its mo- 

 mentum at that moment ? 



53. Compare the momenta of two bodies, masses 4 tons and 4 Ibs, 

 respectively, the former having a velocity of 20 miles an hour and 

 the latter 20 feet per second. 



54. If a mass of 16 Ibs. was moving at the rate of 100 yards a 

 minute and a mass of 4 Ibs. at the rate of 6 miles an hour, find the 

 ratio of the momentum of the first to that of the second. 



55. A bullet, mass 1^ oz., moving horizontally with a velocity of 

 1,248 feet per second, strikes a cubical block of wood, mass 25 Ibs., 

 lying on a smooth horizontal plane, and remains imbedded in it ; 

 find the velocity with which the wood begins to move. 



56. If a 500-lb. shot be fired by a 32-ton gun so that the shot 

 leaves the gun with a velocity of 1,400 feet per second, find the 

 velocity of the gun's recoil. 



57. Just as a tramcar reaches a man standing by the tramway, it 

 has a velocity of 8^ feet per second, the man takes hold of and 

 mounts the car. What change of velocity takes place ? the weights 

 of the car and man being 1 ton and 10 stones respectively. 



58. Two masses are moving with velocities of 12 feet per second 

 and 40 yards per minute respectively ; if their momenta be equal 

 and the mass of one be 6 Ibs., what is the mass of the other? 



59. A mass of 8 Ibs. moves from rest, with an acceleration of 10 feet 

 per second per second ; what is its momentum (a) after 20 seconds,, 

 (b) after it has passed over a distance of 20 feet ? 



60. The same body is weighed by means of a spring balance im 

 London and Rio de Janeiro ; if the weighings show respectively 

 20 Ibs. 1 oz. and 20 Ibs. 2 oz. , compare the values of y obtained. 



61. The intensity of gravity on Jupiter is 2*5 times that on tloie; 

 earth ; find the time it will take a body to fall 160 feeti on 

 Jupiter. 



62. A force F acting on a mass of 10 Ibs. increases its velocity in 

 every second by 10'7 feet per second in a locality where the velocity 

 gained by a falling body in a second of time is 32 '1 feet per second. 

 Compare the magnitude of the force F with the weight of a 

 pound. 



63. Describe an experiment for demonstrating the principle of the- 

 parallelogram of forces to a class. A nail is driven into a wall and' 

 two' strings are tied to its head. When the two strings are pulled! 

 horizontally and at right angles to one another with forces equal to> 

 6 and 8 Ibs. respectively, the nail can be dislodged. What force* 

 would be needed if the strings were brought together and the mauiT 

 pulled straight out ? Illustrate your answer with a diagram. 



64. Two forces, the magnitudes of which are proportional to the 

 numbers 3 and 4, act on a point at right angles to each other. Draw 

 a parallelogram as nearly to a scale as you can to show the direction 

 and magnitude of the resultant, and deduce by measuring your 

 diagram, or in any other way, the magnitude of the resultant. 



65. What is meant by the parallelogram of forces ? Give a diagram* 

 to illustrate your answer. Describe an experiment by means of 

 which the truth of the proposition ma} be verified. 



