A light is on the ground, 15 m from a wall.
A woman, 1.6 m tall, walks away from the light and towards the wall at 0.5 m/s.
Calculate the rate of change of the length of her shadow on the wall
when the woman is 10 m from the wall.
I guess you would have to find the rate at which the tip of her shadow is moving.
. . Right!
* | s
* | |
* |1.6 |
* x | |
: - - - - 15 - - - - - :
From similar right triangles, we have: .
. . and we have: .
Differentiate with respect to time: .
We are given: . . . . and "10 m from the wall" means
. . Therefore: .