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The side of a cube is decreasing at a rate of 9 millimeters per minute.
At a certain instant, the side is 19 millimeters.
What is the rate of change of the volume of the cube at that instant (in cubic millimeters per minute)?
Choose 1 answer:
(A) -3249
(B) -6859
(C) -9747
(D) -729

The side of a cube is decreasing at a rate of 99 millimeters per minute.\newlineAt a certain instant, the side is 1919 millimeters.\newlineWhat is the rate of change of the volume of the cube at that instant (in cubic millimeters per minute)?\newlineChoose 11 answer:\newline(A) 3249-3249\newline(B) 6859-6859\newline(C) 9747-9747\newline(D) 729-729

Full solution

Q. The side of a cube is decreasing at a rate of 99 millimeters per minute.\newlineAt a certain instant, the side is 1919 millimeters.\newlineWhat is the rate of change of the volume of the cube at that instant (in cubic millimeters per minute)?\newlineChoose 11 answer:\newline(A) 3249-3249\newline(B) 6859-6859\newline(C) 9747-9747\newline(D) 729-729
  1. Volume Formula Derivation: The volume of a cube is given by the formula V=s3V = s^3, where ss is the side length of the cube. To find the rate of change of the volume, we need to differentiate the volume with respect to time.
  2. Rate of Change Calculation: So, dVdt=3s2dsdt\frac{dV}{dt} = 3s^2 \cdot \frac{ds}{dt}. Here, dsdt\frac{ds}{dt} is the rate of change of the side length, which is 9mm/min-9\,\text{mm/min} (negative because the side is decreasing).
  3. Substitute Values: Now we plug in the values: s=19mms = 19 \, \text{mm} and dsdt=9mm/min\frac{ds}{dt} = -9 \, \text{mm/min}. So, dVdt=3×(19)2×(9)\frac{dV}{dt} = 3 \times (19)^2 \times (-9).
  4. Final Calculation: Calculating that out, dVdt=3×361×(9)=3×(3249)=9747\frac{dV}{dt} = 3 \times 361 \times (-9) = 3 \times (-3249) = -9747 cubic millimeters per minute.

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