47. A particle moves on the xy-plane so that at time \( t \ge 0 \) its acceleration vector is \( \langle 2,\; e^{-t} \rangle \). When \( t = 0 \), the particle is at rest and its position is \( \langle 3,\;3 \rangle \). At \( t = 2 \) the position of the particle is






Answer is: option4

\( \langle 7,\; 4 + e^{-2} \rangle \)

Solution:

With the acceleration vector \( \mathbf{a}=\langle 2,\;e^{-t}\rangle \), we antidifferentiate to obtain the velocity vector

\[ \mathbf{v}=\langle 2t+A,\;-e^{-t}+B\rangle \]

The particle is at rest when \( t=0 \), so \( \mathbf{v}(0)=\langle 0,0\rangle \).

Since \( \mathbf{v}(0)=\langle 0+A,\;-e^{0}+B\rangle \), we find that \( A=0 \) and \( B=1 \).

Hence \[ \mathbf{v}=\langle 2t,\;1-e^{-t}\rangle \]

We antidifferentiate again to obtain the position vector

\[ \mathbf{s}=\langle t^2+C,\;t+e^{-t}+D\rangle \]

At \( t=0 \), \( \mathbf{s}(0)=\langle 3,3\rangle \), so \( \langle C,\;1+D\rangle=\langle 3,3\rangle \), and therefore \( C=3 \), \( D=2 \).

\[ \mathbf{s}=\langle t^2+3,\;t+e^{-t}+2\rangle \]

When \( t=2 \), \[ \mathbf{s}=\langle 7,\;4+e^{-2}\rangle \]

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