Integrating Vector-Valued Functions
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AP Calculus BC › Integrating Vector-Valued Functions
A particle’s acceleration is $\vec a(t)=\langle 6t,,-4\rangle$ with $\vec v(0)=\langle 1,2\rangle$; find $\vec v(t)$.
$\vec v(t)=\langle 3t^2+1,,-4t+2\rangle$
$\vec v(t)=\langle 3t^2+2,,-4t+1\rangle$
$\vec v(t)=\langle 3t^2,,-4t\rangle$
$\vec v(t)=\langle 3t^2+1,,-4t-2\rangle$
$\vec v(t)=\langle 6t^2+1,,-4t+2\rangle$
Explanation
This problem requires integrating a vector-valued acceleration to find velocity, a key skill in vector calculus. To solve, integrate each component separately, starting with the x-component where ∫6t dt is 3t² plus a constant. For the y-component, ∫-4 dt is -4t plus a constant. Apply the initial condition at t=0 to get constants 1 and 2, resulting in ⟨3t² + 1, -4t + 2⟩. A tempting distractor like choice B omits the constants, ignoring the initial velocity. Always integrate vector functions component-wise and incorporate initial conditions to find the specific solution.
Compute $\int \langle e^t,,\frac{1}{1+t^2}\rangle,dt$ as an antiderivative vector.
$\langle e^t+C,,\arctan(t)+C\rangle$
$\langle te^t+C_1,,\arctan(t)+C_2\rangle$
$\langle e^t,,\arctan(t)\rangle$
$\langle e^t+C_1,,\ln(1+t^2)+C_2\rangle$
$\langle e^t+C_1,,\arctan(t)+C_2\rangle$
Explanation
This problem requires finding the indefinite integral of a vector-valued function, a key skill in vector calculus. To solve, integrate each component separately, with the x-component where $∫e^t$ dt is $e^t$ plus a constant C1. For the y-component, ∫1/(1 + t²) dt is arctan t plus a constant C2. This gives the antiderivative $⟨e^t$ + C1, arctan t + C2⟩. A tempting distractor like choice D substitutes ln(1 + t²) for arctan t, but its derivative is 2t/(1 + t²), not matching. Always integrate vector functions component-wise, recalling standard antiderivatives like arctan for 1/(1 + t²) and including separate constants.
Evaluate $\displaystyle \int_{0}^{2}\langle(t-1)^{2},,\frac{1}{1+t},,\sin(\pi t)\rangle,dt$.
$\left\langle \frac{8}{3},,\ln 3,,0\right\rangle$
$\left\langle \frac{2}{3},,\ln 3,,\frac{2}{\pi}\right\rangle$
$\left\langle \frac{2}{3},,\ln 3,,0\right\rangle$
$\left\langle \frac{2}{3},,\ln 2,,0\right\rangle$
$\left\langle \frac{2}{3},,\frac{1}{3},,0\right\rangle$
Explanation
This problem requires evaluating a definite integral of a vector function. For the first component: ∫₀² (t-1)² dt = ∫₀² (t² - 2t + 1) dt = [t³/3 - t² + t]₀² = 8/3 - 4 + 2 = 2/3. For the second component: ∫₀² 1/(1+t) dt = [ln|1+t|]₀² = ln 3 - ln 1 = ln 3. For the third component: ∫₀² sin(πt) dt = [-(1/π)cos(πt)]₀² = -(1/π)(cos 2π - cos 0) = 0. Choice C incorrectly evaluates the first component as 8/3, perhaps computing only the t³/3 term. When integrating polynomials, expand first and integrate term by term to avoid errors.
A particle has velocity $\vec v(t)=\langle 2t,\cos t,3\rangle$ and position $\vec r(0)=\langle 1,0,-2\rangle$; find $\vec r(t)$.
$\vec r(t)=\langle t^2,\sin t,-2+3t\rangle$
$\vec r(t)=\langle t^2+1,\sin t,-2+3t\rangle$
$\vec r(t)=\langle 2t^2+1,\sin t,-2+3t\rangle$
$\vec r(t)=\langle t^2+1,\sin t,-2+t^3\rangle$
$\vec r(t)=\langle t^2+1,-\sin t,-2+3t\rangle$
Explanation
This problem involves integrating a vector-valued velocity function to find the position function. For the x-component, integrate 2t with respect to t to obtain t² plus a constant. For the y-component, integrate cos t to get sin t plus a constant. For the z-component, integrate 3 to yield 3t plus a constant, then use the initial position at t=0 to solve for the constants, resulting in +1, +0, and -2 respectively. A tempting distractor like choice B includes 2t² +1 for the x-component, which fails because it incorrectly doubles the integral of 2t instead of properly computing t². When integrating vector functions, always perform component-wise integration and apply initial conditions to determine the constant vector.
Evaluate $\int_0^2 \langle 3t^2,,4,,e^t\rangle,dt$ as a vector.
$\left\langle 4,,8,,e^2-1\right\rangle$
$\left\langle 8,,8,,e^2\right\rangle$
$\left\langle 8,,8,,e^2-1\right\rangle$
$\left\langle 12,,8,,e^2-1\right\rangle$
$\left\langle 8,,4,,e^2-1\right\rangle$
Explanation
This problem requires evaluating a definite integral of a vector-valued function from 0 to 2. For the x-component, integrate 3t² to get t³ evaluated from 0 to 2, yielding 8. For the y-component, integrate 4 to obtain 4t evaluated from 0 to 2, resulting in 8. For the z-component, integrate $e^t$ to $e^t$ evaluated from 0 to 2, giving e² - 1. A tempting distractor like choice B shows 12 for the x-component, which fails because it mistakenly uses 4t³/4 instead of t³ for the antiderivative of 3t². Remember, for vector integrals, compute each component's definite integral separately and combine them into the resulting vector.
Evaluate $\displaystyle \int_{0}^{\pi}\langle \sin t,,2t,,3\rangle,dt$.
$\left\langle -2,,\pi^{2},,3\pi\right\rangle$
$\left\langle 2,,\frac{\pi^{2}}{2},,3\pi\right\rangle$
$\left\langle 2,,\pi^{2},,3\pi\right\rangle$
$\left\langle 2,,2\pi,,3\pi\right\rangle$
$\left\langle 0,,\pi^{2},,3\right\rangle$
Explanation
This problem involves evaluating a definite integral of a vector-valued function. We integrate each component separately over the interval [0, π]: ∫₀^π sin t dt = [-cos t]₀^π = -cos π - (-cos 0) = -(-1) - (-1) = 2. For the second component: ∫₀^π 2t dt = [t²]₀^π = π² - 0 = π². For the third component: ∫₀^π 3 dt = [3t]₀^π = 3π - 0 = 3π. Choice C incorrectly evaluates the second component as 2π instead of π², confusing the antiderivative of 2t. When integrating vector functions, apply the fundamental theorem of calculus to each component separately.
A particle has $\vec v(t)=\langle e^{t},,\sin t,,2t\rangle$ and $\vec r(0)=\langle 0,1,-3\rangle$; find $\vec r(t)$.
$\vec r(t)=\langle e^{t},,-\cos t+1,,t^{2}-3\rangle$
$\vec r(t)=\langle e^{t}-1,,-\cos t+2,,t^{2}-3\rangle$
$\vec r(t)=\langle e^{t},,-\cos t+2,,t^{2}-3\rangle$
$\vec r(t)=\langle e^{t}-1,,-\cos t,,t^{2}-3\rangle$
$\vec r(t)=\langle e^{t}-1,,\cos t+1,,2t^{2}-3\rangle$
Explanation
This problem requires finding position from velocity with an initial condition. Integrating the velocity components: $∫e^t$ dt = $e^t$ + C₁, ∫sin t dt = -cos t + C₂, and ∫2t dt = t² + C₃. Applying r⃗(0) = ⟨0, 1, -3⟩: $e^0$ + C₁ = 0 gives C₁ = -1; -cos 0 + C₂ = 1 gives C₂ = 2; and 0² + C₃ = -3 gives C₃ = -3. Choice A incorrectly calculates C₂ = 1 instead of C₂ = 2, missing that -cos 0 = -1. The crucial step in initial value problems is carefully evaluating each component at t = 0 to find the correct constants.
Compute $\int_0^{\pi} \langle \cos t,,\sin t,,2t\rangle,dt$ as an ordered triple.
$\left\langle 0,,0,,2\pi\right\rangle$
$\left\langle 0,,2,,2\pi\right\rangle$
$\left\langle 2,,0,,\pi^2\right\rangle$
$\left\langle 0,,2,,\pi^2\right\rangle$
$\left\langle 0,,0,,\pi^2\right\rangle$
Explanation
This problem requires computing a definite integral of a vector-valued function from 0 to π. For the x-component, integrate cos t to sin t evaluated from 0 to π, yielding 0. For the y-component, integrate sin t to -cos t evaluated from 0 to π, resulting in 2. For the z-component, integrate 2t to t² evaluated from 0 to π, giving π². A tempting distractor like choice A shows 0 for y, which fails because it neglects the sign change in evaluating -cos t at the limits. When performing definite integrals on vectors, integrate and evaluate each component separately to form the final vector.
A particle has velocity $\vec v(t)=\langle 4\cos t,,5\sin t\rangle$ and $\vec r(0)=\langle -1,3\rangle$; find $\vec r(t)$.
$\vec r(t)=\langle 4\sin t-1,,-5\cos t+8\rangle$
$\vec r(t)=\langle 4\cos t-1,,5\sin t+3\rangle$
$\vec r(t)=\langle 4\sin t+1,,-5\cos t+8\rangle$
$\vec r(t)=\langle -4\sin t-1,,-5\cos t+8\rangle$
$\vec r(t)=\langle 4\sin t-1,,5\cos t+3\rangle$
Explanation
This problem involves integrating trigonometric velocity components to find position. Integrating $\vec{v}(t) = \langle 4\cos t, 5\sin t \rangle$ gives $\vec{r}(t) = \langle 4\sin t + C_1, -5\cos t + C_2 \rangle$. Using $\vec{r}(0) = \langle -1, 3 \rangle$: we get $4\sin(0) + C_1 = -1$, so $C_1 = -1$, and $-5\cos(0) + C_2 = 3$, so $C_2 = 8$. Choice D incorrectly has $5\cos t$ instead of $-5\cos t$, forgetting the negative sign when integrating sine. Remember that $\int \sin t,dt = -\cos t + C$, and apply initial conditions after integration.
Compute $\int \langle 5\cos t,, -4\sin t\rangle,dt$ as a vector-valued function.
$\langle 5\cos t + C_1,, -4\sin t + C_2\rangle$
$\langle -5\sin t + C_1,,4\cos t + C_2\rangle$
$\langle 5\sin t + C_1,,-4\cos t + C_2\rangle$
$\langle 5\sin t + C_1,,4\cos t + C_2\rangle$
$\langle 5\sin t + C,,4\cos t + C\rangle$
Explanation
This problem asks for the indefinite integral of a vector-valued trigonometric function. Integrating component by component: ∫5cos t dt = 5sin t + C₁ and ∫(-4sin t) dt = 4cos t + C₂. The antiderivative is ⟨5sin t + C₁, 4cos t + C₂⟩. Choice E incorrectly shows -4cos t for the y-component, which would result from forgetting that integrating -sin t gives +cos t (the negative sign is already accounted for). When integrating vector functions, carefully track signs and remember that each component needs its own integration constant.