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The perimeter of a square is increasing at a rate of 5 meters per hour.
At a certain instant, the perimeter is 30 meters.
What is the rate of change of the area of the square at that instant (in square meters per hour)?
Choose 1 answer:
(A) 
(5)/(4)
(B) 25
(C) 
(75)/(4)
(D) 
(25)/(16)

The perimeter of a square is increasing at a rate of 55 meters per hour.\newlineAt a certain instant, the perimeter is 3030 meters.\newlineWhat is the rate of change of the area of the square at that instant (in square meters per hour)?\newlineChoose 11 answer:\newline(A) 54 \frac{5}{4} \newline(B) 2525\newline(C) 754 \frac{75}{4} \newline(D) 2516 \frac{25}{16}

Full solution

Q. The perimeter of a square is increasing at a rate of 55 meters per hour.\newlineAt a certain instant, the perimeter is 3030 meters.\newlineWhat is the rate of change of the area of the square at that instant (in square meters per hour)?\newlineChoose 11 answer:\newline(A) 54 \frac{5}{4} \newline(B) 2525\newline(C) 754 \frac{75}{4} \newline(D) 2516 \frac{25}{16}
  1. Calculate Perimeter Length: First, let's find the length of one side of the square using the perimeter. The perimeter PP of a square is 44 times the length of one side ss, so P=4sP = 4s.
  2. Solve for Side Length: Given P=30P = 30 meters, we can solve for ss: 30=4s30 = 4s, so s=304=7.5s = \frac{30}{4} = 7.5 meters.
  3. Find Area: Now, we know the area AA of a square is s2s^2. So, A=(7.5)2=56.25A = (7.5)^2 = 56.25 square meters.
  4. Perimeter Rate of Change: The rate of change of the perimeter is 55 meters per hour. Since the perimeter is 44 times the length of one side, the rate of change of the length of one side is 54\frac{5}{4} meters per hour.
  5. Area Rate of Change: To find the rate of change of the area, we use the derivative of AA with respect to ss, which is dAds=2s\frac{dA}{ds} = 2s. Then we multiply this by the rate of change of ss, which is dsdt\frac{ds}{dt}.
  6. Final Rate of Change: So, the rate of change of the area is dAdt=dAdsdsdt=2s(54)\frac{dA}{dt} = \frac{dA}{ds} \cdot \frac{ds}{dt} = 2s \cdot \left(\frac{5}{4}\right).
  7. Final Rate of Change: So, the rate of change of the area is dAdt=dAdsdsdt=2s(54)\frac{dA}{dt} = \frac{dA}{ds} \cdot \frac{ds}{dt} = 2s \cdot \left(\frac{5}{4}\right). Plugging in the value of ss, we get dAdt=27.5(54)=15(54)=18.75\frac{dA}{dt} = 2 \cdot 7.5 \cdot \left(\frac{5}{4}\right) = 15 \cdot \left(\frac{5}{4}\right) = 18.75 square meters per hour.

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