Problem

A cylinder begins with a diameter of 28 yards and a height of 22 yards. If the diameter increases at an instantaneous rate of $2 \mathrm{yd} / \mathrm{sec}$ and the height decreases at an instantaneous rate of $-5 \mathrm{yd} / \mathrm{sec}$, determine the rate at which the surface area of the cylinder is changing.

Answer

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Answer

So, the rate at which the surface area of the cylinder is changing is \(\boxed{60\pi \, \text{yd}^2/\text{sec}}\).

Steps

Step 1 :We are given a cylinder with a diameter of 28 yards and a height of 22 yards. The diameter is increasing at a rate of 2 yards per second and the height is decreasing at a rate of 5 yards per second. We are asked to find the rate at which the surface area of the cylinder is changing.

Step 2 :The surface area of a cylinder is given by the formula \(A = 2\pi r(r + h)\), where \(r\) is the radius and \(h\) is the height.

Step 3 :We can differentiate the surface area formula with respect to time to get an expression for the rate of change of the surface area. This will give us a formula in terms of the rates of change of the radius and the height.

Step 4 :Taking the derivative, we get \(\frac{dA}{dt} = 2\pi\frac{dh}{dt}r + \frac{dr}{dt}(2\pi r + 2\pi(h + r))\).

Step 5 :We substitute the given values into the formula: \(r = 14\), \(h = 22\), \(\frac{dr}{dt} = 2\), and \(\frac{dh}{dt} = -5\).

Step 6 :Substituting these values in, we find that \(\frac{dA}{dt} = 60\pi\).

Step 7 :So, the rate at which the surface area of the cylinder is changing is \(\boxed{60\pi \, \text{yd}^2/\text{sec}}\).

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