A particle moves in the plane with position vector

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

Problem

A particle moves in the plane with position vector r(t)\mathbf r(t). Which of the following statements correctly identifies the condition under which the particle is at rest? (a) r(t)=⟨0,0⟩\mathbf r(t)=\langle 0,0\rangle (b) ddt∥r(t)∥=0\displaystyle \frac{d}{dt}\lVert\mathbf r(t)\rVert=0 (c) ∥r′(t)∥=0\lVert\mathbf r'(t)\rVert=0 (d) r′′(t)=⟨0,0⟩\mathbf r''(t)=\langle 0,0\rangle

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