Question

The volume v of a cylinder is computed using the values 2.2 m for diameter and 6.8 m for height. use the linear approximation to estimate the maximum error in v if each of these values has a possible error of at most 5% (use decimal notation. give your answer to three decimal places.)

Answer 1

A linear approximation to the error in volume can be written as

... ∆V = (∂V/∂d)·∆d + (∂V/∂h)·∆h

For V=(π/4)·d²·h, this is

... ∆V = 2·(π/4)·d·h·∆d + (π/4)·d²·∆h

Using ∆d = 0.05d and ∆h = 0.05h, this becomes

... ∆V = (π/4)·d²·h·(2·0.05 + 0.05) = 0.15·V

The nominal volume is

... V = (π/4)·d²·h = (π/4)·(2.2 m)²·(6.8 m) = 25.849 m³

Then the maximum error in volume is

... 0.15V = 0.15·25.849 m³ ≈ 3.877 m³

_____

Essentially, the error percentage is multiplied by the exponent of the associated variable. Then these products are added to get the maximum error percentage.