1. A spotlight is on the ground 100 feet from a vertical building.
A 6-foot man starts at the spotlight and walks towards the building at 5 ft/sec.
| * A
y | | *
| |6 *
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* - - - * - - - - - - - * - -
D x B 100-x L
: - - - - 100 - - - - - :
The spotlight is at
The man is: .
His shadow is: .
His distance from the building is: .
. . Hence: .
We are given: . ft/sec.
From similar right triangles
. . Then: .
Differentiate with respect to time: .
. . and we have: .
When . . . a) How fast is the top of the man's shadow moving down the building
when he is 50 feet from the building?
When . . . b) How fast is the top of the man's shadow moving down the building
when he is 25 feet from the building?