\fdO'^ - Old Forge Coal Mines

ELEMENTARY MECHANICS. 173
(392)
W
Using formula 10, m = —, W=mg= 63.7 X
32.16 = 1,727 lb. Ans.
(393) {a) Yes. {b) 25. {c)
(394) {a) Using formula \Z, '.
25. Ans.
d"" \ R' :: W
w,
d =
V — r -^— T7^ = 4,749.736 miles. 4,749.736 —
w 100
4,000=749.736 miles. Ans.
(^) Using formula 11, R :
d :: W :
w, d = -jrr =
4,000 X 100 _ 2 g36,88 miles. 4,000 - 2,836.88 = 1,163.12
141
miles. Ans.
(396) (a) Use formula 18,
. ./27i ./2 X .
5,280
t=y — =y — — = ,.„ 18.12 sec. Ans.
5^5-7^
{b) Use formula 13, 2^=^/ = 32. 16X18. 12 = 582. 74 ft. per
sec, or, by formula 1 6, ^^ = V%gh = V^ X 32.16 X 5,280 =
582.76 ft. per sec. Ans.
The slight difference in the two velocities is caused by not
calculating the time to a sufficient number of decimal places,
the actual value for / being 18.12065 sec.
(396) Use formula 26. Kinetic energy = Wh = —— .
Wh = 160 X 5,280 = 844,800 ft. -lb.
Wif 100X582.76' oAA»a(^(^ ^u a
-1^— = — n rriTTTr- = 844, 799 ft. -lb. Ans,
'
2 X 32.16
2^
(397) (a) Using formulas 16 and 14,
h= i- = , '7^,, = 86,592 ft. = 16.4 miles. Ans. '
'Zg 2 X 32.16
{b) '
t = -^=1 time required to go up or fall back. Hence, total
time = — sec. = ,.^ .. 00 ... = 2.4461 mm. = 2 mm. 26.77
g
sec. Ans.
60 X o2.1d