A street light is mounted at the top of a 15 foot tall pole. A man 6 ft tall walks away from the pole with a speed of 6 ft/s along a straight path. How fast is the tip of his shadow moving when he is 40 ft from the pole?
2006-10-16 14:42:06 · 3 answers · asked by Anonymous in Science & Mathematics ➔ Mathematics
If s = distance from pole to man and h = length of shadow, by similar triangles 15/(s+h) = 6/h
6s + 6h = 15h
6s = 9h
h = 2/3 s
dh/ds = 2/3
ds/dt = 6
dh/dt = dh/ds times ds/st = 6 times 2/3 = 4 ft/s
which doesn't make sense, wait a min....
Yes it does, you just have to add it to 6 ft/sec to get the tip's speed which is 10 ft/sec. no matter how far away
2006-10-16 15:03:49 · answer #1 · answered by hayharbr 7 · 0⤊ 0⤋
10'/s it's constant.
2006-10-16 21:58:01 · answer #2 · answered by feanor 7 · 0⤊ 0⤋
i dunno
2006-10-16 21:49:27 · answer #3 · answered by Bookworm 2 · 0⤊ 2⤋