The volume of a cube is increasing at a rate of 18 cubic meters per hour.At a certain instant, the volume is 8 cubic meters.What is the rate of change of the surface area of the cube at that instant (in square meters per hour)?Choose 1 answer:(A) 23(B) 24(C) 36(D) (318)2
Q. The volume of a cube is increasing at a rate of 18 cubic meters per hour.At a certain instant, the volume is 8 cubic meters.What is the rate of change of the surface area of the cube at that instant (in square meters per hour)?Choose 1 answer:(A) 23(B) 24(C) 36(D) (318)2
Find side length: First, find the side length of the cube when the volume is 8 cubic meters. The formula for the volume of a cube is V=s3, where s is the side length.
Calculate side length: Calculate the side length: 8=s3. So, s=38, which is 2 meters.
Find surface area: Now, find the surface area of the cube using the side length. The formula for the surface area of a cube is SA=6s2.
Calculate surface area: Calculate the surface area: SA=6×(22)=6×4=24 square meters.
Find rate of change: Next, find the rate of change of the side length as the volume increases. The formula for the volume of a cube is V=s3, so dtdV=3s2⋅dtds, where dtdV is the rate of change of volume and dtds is the rate of change of the side length.
Calculate rate of change: Plug in the known values: 18=3×(22)×dtds. So, 18=3×4×dtds, which means dtds=1218=1.5 meters per hour.
Find rate of change: Finally, find the rate of change of the surface area. The formula for the surface area of a cube is SA=6s2, so dtdSA=6×2s×dtds.
Calculate rate of change: Plug in the known values: dtdSA=6×2×2×1.5. So, dtdSA=6×4×1.5=36 square meters per hour.
Final answer: The correct answer is (C) 36 square meters per hour.
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