4. Applications of Derivatives

A sphere is growing at a rate of $50\(\frac{\operatorname{\mathrm{cm}\)}^3}{s}$. At what rate is the radius of the sphere increasing when the radius is $5\(\operatorname{\mathrm{cm}\)}$?

A right triangle has a base of and a height of . The height of the right triangle is decreasing at a rate of , at what rate is the area of the triangle decreasing?

The perimeter of a rectangle is fixed at . If the length $L$ is increasing at a rate of , for what value of $L$ does the area start to decrease? Hint: the rectangle's area starts to decrease when the rate of change for the area is less than 0.

A 15-foot plank leans against a vertical pole. The top of the plank begins to slide down the pole at a steady speed of 2 inches per second. How fast is the bottom of the plank moving away from the pole when it is 8 feet away from the base of the pole (in inches per second)?