ENERGY. 85 



10. (.) Why is it that a lead ball and a wooden ball will fall 100 

 feet in the same time? (&.) How did Galileo study the laws of 

 falling bodies? (c.) Who was Galileo and when did he live? (d.) 

 Define increment of velocity. 



11. (a.) Give the laws of freely falling bodies. (&.) Express the 

 same truths algebraically, (c.) What forces act upon a projectile ? 

 (d.) Define random. 



12. (a.) What is a simple pendulum? (&.) A compound pen- 

 dulum? (e.) What is the real length of a pendulum? (d.) How 

 long must a pendulum be to vibrate once a minute ? (e.) Once a 

 second ? (/. ) What is the most important property of a pendulum ? 



13. Two forces of 6 and 8 pounds respectively act at right angles 

 to each other. Find the direction and intensity of their equilibrant. 



14. (.) Define energy. (&.) Foot-pound, (c.) Horse-power, (d.) 

 Give the rule for calculating horse-power. 



15. (.) What is a kilogram-meter? (&.) Give the formula for 

 the calculation of kinetic energy from weight and velocity, (c.) 

 Deduce the same. 



16. (a.) State fully and clearly the difference between kinetic and 

 potential energy. (&.) Illustrate the same by the pendulum. 



17. (a.) What is the object of experiments in the study of phy- 

 sics? (6.) What is the metric unit of weight? (c.) How is it ob- 

 tained ? 



18. Three inelastic balls weighing 5, 7 and 8 pounds, lie in the 

 same straight line. The first strikes the second with a velocity of 

 60 feet per second ; the first and second together strike the third. 

 What will be the velocity of the third ? 



