30 



FORCE AND MOTION. 



two ball pendulums, one of which weighs twice as much 



as the other, suspended as 

 represented. The heavier ball 

 contains a spring-hammer, 

 which is held back by a thread. 

 The hammer being thus held 

 back, and the smaller ball 

 resting against its face, the 

 thread is burned, a blow is 

 struck, and an equal force is 

 exerted upon each ball ( 72 

 [3] and 93). The smaller ball 

 will move twice as fast and 

 twice as far as the larger ball, 



FIG. 6. 



equal forces producing equal momenta. 

 EXERCISES. 



1. Find the momentum of a 500 Ib. ball moving 500 feet a second. 



2. By falling a certain time, a 200 Ib. ball lias acquired a velocity 

 of 321.6 ft. What is its momentum ? 



8. A boat, that is moving at the rate of 5 miles an hour, weighs 

 4 tons; another, that is moving at the rate of 10 miles an hour, 

 weighs 2 tons. How do their momenta compare? 



4. What is meant by a force of 10 pounds ? To how many kinetic 

 units is it equal ? 



5. A stone weighing 12 oz. is thrown with a velocity of 1320 ft. 

 per minute. An ounce ball is shot with a velocity of 15 miles per 

 minute. Find the ratio between their momenta. 



6. An iceberg of 50,000 tons moves with a velocity of 2 miles an 

 hour ; an avalanche of 10,000 tons of snow descends with a velocity 

 of 10 miles an hour. Which has the greater momentum ? 



7. Two bodies weighing respectively 23 and 40 pounds have equal 

 momenta. The first has a velocity of 60 ft. a second ; what is the 

 velocity of the other ? 



8. Two balls have equal momenta. .The first weighs 100 kilo- 



