William was given this problem:The radius r(t) of a sphere is increasing at a rate of 7.5 meters per minute. At a certain instant t0, the radius is 5 meters. What is the rate of change of the surface areaS(t) of the sphere at that instant?Which equation should William use to solve the problem?Choose 1 answer:(A) S(t)=2π⋅r(t)(B) S(t)=π[r(t)]2(C) S(t)=4π[r(t)]2(D) S(t)=34π[r(t)]3
Q. William was given this problem:The radius r(t) of a sphere is increasing at a rate of 7.5 meters per minute. At a certain instant t0, the radius is 5 meters. What is the rate of change of the surface area S(t) of the sphere at that instant?Which equation should William use to solve the problem?Choose 1 answer:(A) S(t)=2π⋅r(t)(B) S(t)=π[r(t)]2(C) S(t)=4π[r(t)]2(D) S(t)=34π[r(t)]3
Identify Formula: Identify the correct formula for the surface area of a sphere.The surface area S(t) of a sphere with radius r(t) is given by the formula S(t)=4π[r(t)]2. This is because the surface area of a sphere is 4 times π times the square of the radius.
Determine Correct Option: Determine which of the given options corresponds to the correct formula for the surface area of a sphere.(A) S(t)=2π⋅r(t) is the formula for the circumference of a circle, not the surface area of a sphere.(B) S(t)=π[r(t)]2 is the formula for the area of a circle, not the surface area of a sphere.(C) S(t)=4π[r(t)]2 is the correct formula for the surface area of a sphere.(D) S(t)=34π[r(t)]3 is the formula for the volume of a sphere, not the surface area.Therefore, the correct equation that William should use to solve the problem is (C) S(t)=4π[r(t)]2.
Calculate Rate of Change: Calculate the rate of change of the surface area S(t) with respect to time t. To find the rate of change of the surface area with respect to time, we need to differentiate the surface area function S(t) with respect to time t. This is done using the chain rule of differentiation. dtdS=dtd[4π[r(t)]2]=4π⋅2r(t)⋅dtdr
Substitute Given Values: Substitute the given rate of change of the radius and the radius at the instant t0. We are given that the radius r(t) is increasing at a rate of dtdr=7.5 meters per minute and that at the instant t0, the radius r(t) is 5 meters. dtdS=4π×2×5 meters ×7.5 meters/minute =4π×10×7.5 meters2/minute
Perform Calculation: Perform the calculation to find the rate of change of the surface area. dtdS=4π×10×7.5 meters2/minute =300π meters2/minute This is the rate of change of the surface area of the sphere at the instant when the radius is 5 meters.
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