Question

A ladder 10 ft long leans against a vertical wall. If the lower end is being moved away from the wall at the rate of 6 ​ft/sec, how fast is the height of the top changing​ (this will be a negative​ rate) when the lower end is 6 feet from the​ wall?

Answer 1

-4.5ft per sec

Explanation:

Assume that vertical wall has a distance of y and the horizontal floor is x (6 ft).

This forms a triangle with the ladder as the hypothenus of length 10ft

We have dy/dt = 6ft per sec

According to Pythagoras law the relationship between x and y is

(x^2) + (y^2) = (hypothenus ^2) = 10^2

When we differentiate both sides of the equation

2x(dx/dt) + 2y(dy/dt) = 0

dy/dt = (x/y) * (dx/dt)

y= √(10^2) - (6^2) = 8ft

So dy/dt = (6/8)* (6/1)= -4.5 ft per sec

It is a negative rate