Exercise · ZW-SCALAR-LINE-INTEGRAL-004 · ★☆☆ Basic
Compute \(\int_C (x^2+y^2)\,ds\) on the circle \(\mathbf r(t)=\langle 3\cos t,3\sin t\rangle\), \(0\le t\le2\pi\).
Choose one option.
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- C. \(54\pi\)
Explanation
On the curve \(x^2+y^2=9\) and \(\|\mathbf r'\|=3\), so the value is \(9\cdot3\cdot2\pi=54\pi\): the constant \(f\) times the length \(6\pi\).
Review the concept: Line integral of a scalar function
The line integral of a scalar function \(f\) over a curve \(C\) parametrized by \(\mathbf r(t)\), \(a\le t\le b\), accumulates the values of \(f\) weighted by the arc length \(ds\).
\[\int_C f\,ds=\int_a^b f(\mathbf r(t))\,\|\mathbf r'(t)\|\,dt\]
More practice problems: line integral of a scalar function
- ZW-SCALAR-LINE-INTEGRAL-001 Compute ∫_C 2 ds, with C the segment mathbf r(t)=langle 3t,4trangle, 0≤ t≤1.
- ZW-SCALAR-LINE-INTEGRAL-002 Compute ∫_C x ds, with mathbf r(t)=langle t,2trangle, 0≤ t≤1.
- ZW-SCALAR-LINE-INTEGRAL-003 Compute ∫_C xy ds over the arc mathbf r(t)=langlecos t,sin trangle, 0≤ t≤π/2.
- ZW-SCALAR-LINE-INTEGRAL-005 If the orientation of C is reversed, what happens to ∫_C f ds?
- ZW-SCALAR-LINE-INTEGRAL-006 Compute the length of the curve mathbf r(t)=langle 2t,3t,6trangle, 0≤ t≤1, as ∫_C 1 ds.
- ZW-SCALAR-LINE-INTEGRAL-007 Compute ∫_C y ds on the upper semicircle mathbf r(t)=langlecos t,sin trangle, 0≤ t≤π.
- ZW-SCALAR-LINE-INTEGRAL-008 Compute ∫_C x ds on the parabola mathbf r(t)=langle t,t^2rangle, 0≤ t≤1.
- ZW-SCALAR-LINE-INTEGRAL-009 Compute ∫_C z ds on the helix mathbf r(t)=langlecos t,sin t,trangle, 0≤ t≤2π.