Under a -ft streetlamp

MATHEMATICS · Single correct · AP · Calculus AB · Contextual Applications of Differentiation · Contextual Applications of Differentiation

Problem

Under a

20

-ft streetlamp, a

5

-ft tall runner moves directly away from the lamp. At the moment the runner is

15\text{ ft}

from the base, the tip of the runner’s shadow is moving at

8\text{ ft/s}

. How fast is the runner moving at that instant? (a)

8\text{ ft/s}

(b)

6\text{ ft/s}

(c)

12\text{ ft/s}

(d)

6.4\text{ ft/s}