50. A particle moves in the xy-plane so that its velocity vector at time \( t \ge 0 \) is \[ \mathbf{v}(t)=(2t,\sin t) \] and the particle's position vector at time \( t=0 \) is \( (0,1) \). The position vector of the particle when \( t=\pi \) is






Answer is: option2

\( (\pi^2,\;3) \)

Solution:

\[ \mathbf{v}(t)=\langle 2t,\sin t \rangle \quad \Rightarrow \quad \mathbf{s}(t)=\langle t^2+C,\,-\cos(t)+D \rangle \]

\[ \mathbf{s}(0)=\langle C,\,-1+D \rangle \]

Since we are given that \[ \mathbf{s}(0)=\langle 0,1 \rangle, \] we determine that \( C=0 \) and \( D=2 \).

Then \[ \mathbf{s}(t)=\langle t^2,\;2-\cos(t) \rangle \]

We then compute \[ \mathbf{s}(\pi)=\langle \pi^2,\;2-\cos(\pi) \rangle =\langle \pi^2,\;3 \rangle \]

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