(360 = -5 6^ whence g = 20 m. per second.)
2

269. What was the space passed over by the body in the
previous example during the last second ?

(If in 6 seconds it describes 360 m, it will in five seconds

describe — , 5^ = 250 m., and in the sixth second it will pass
2

over 360 — 250 = no meters.)

270. A canon ball was projected vertically upward with a
velocity of 500 meters per second. After how many seconds
was its velocity reduced to 300 m. (under the retarding influ-
ence of gravity), and what space had it passed over ? (g =
10 m.)

271. A body impressed with an initial velocity, whose
amount or intensity is unknown, is acted upon by a retarding
force of 20 m. per second in the opposite direction, in conse-
quence of which it comes to rest at the end of 30 seconds.
Find the intensity of the initial velocity.
ENEKGY. 35



ENERGY.
(Formula of Kinetic Energy = ^wz^*, in which m = the

W
mass (or — ) of the moving body, v == its velocity per sec.)

g

280. State what is meant by energy, by kinetic energy, and

by i)otential energy.
