When recovering a position vector from a known velocity vector by integration

MATHEMATICS · Single correct · AP · Calculus BC · Parametric, Polar, and Vector-Valued Functions · Parametric, Polar, and Vector-Valued Functions

Problem

When recovering a position vector r(t)\mathbf r(t) from a known velocity vector v(t)\mathbf v(t) by integration, which of the following statements best justifies the appearance of an additional constant vector C\mathbf C in r(t)=∫v(t) dt+C\mathbf r(t)=\displaystyle \int \mathbf v(t)\,dt+\mathbf C? (a) C\mathbf C represents the initial velocity carried through a second integration, because two integrations are required to go from acceleration to position. (b) The constant vector C\mathbf C is added only when the particle does not start at the origin; if r(0)=0\mathbf r(0)=\mathbf 0, no constant is needed. (c) Each antiderivative of v(t)\mathbf v(t) differs by a constant vector, so C\mathbf C accounts for all possible initial positions. (d) Integrating each component of v(t)\mathbf v(t) introduces a separate scalar constant, which are collected into a single vector C\mathbf C only when the component functions of v(t)\mathbf v(t) are non-zero.

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