0. S. 19



290 ANSWERS TO QUESTIONS

CHAP.
V. 2. The sound travels the whole length of the column in the

time the men take to make 2 steps, i.e. it travels 1080 ft.
. 60 X 2 , 1080 X 128 , , .„ ,,

m sec. ; whence v= — gjr — = — = 1152 ft. per sec.
. 1200 s/x° + 27S° , ,_„„

4. TPion = — / ' whence x = 58° C.
1090 \/273°

6. 20-9 ft.
7. Frequency 250. Wave-length 136 cm.
11. 1-37:1.
VI. 2. The path taken by the echo must he 1100 ft. greater than

the distance between the men, whence by geometry we find
the distance of the men from the wall is 923 ft. The
interval is greater on a cold day.
3. The period of the note heard is the time taken by the sound
in travelling twice the distance between two adjacent
posts. Taking the velocity of sound to be 1100 ft. per sec,
the frequency is 550.
12. The interval is '95 sec.
VII. 5. The ratio of the frequencies is in each case 15 : 16, whence

the differences of the frequencies are 3-3, 16"7 and 66'7
respectively.
6. First Difference Tone 50. Second Difference Tones 50 and
100. Summation Tone 250.
10. If the person who carries the fork is the listener, he will hear

9'2 beats per sec. A stationary listener in the line of
motion of the fork hears no beats when the fork is ap-
proaching him, and 9-2 per sec. after it has passed him.
11. 336f metres per sec.
