A 17 ft ladder is leaning against a wall.

Question

If the bottom of the ladder is pulled along the ground away from the wall at a rate of 2ft/sec, how fast will the top of the ladder be moving down the wall when it is 8 ft above the ground?

Answer 1

x^2 + y^2 = 289

2x x' + 2y y' = 0

when y=8 , x = 15

2(15)(2) + 2(8) y ' = 0

60 + 16y' = 0

16y' = -60

y ' = 60/16 = 30/8 = 15/4