Solution 8.4b

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Here we have \displaystyle \mathbf{a}=0\textrm{.}2\mathbf{i}+0\textrm{.}3\mathbf{j},\ \ \displaystyle \mathbf{u}=4\mathbf{i}– 8\mathbf{j}\ \ and \displaystyle \ \ \mathbf{ r}_{0}=6\mathbf{i}+2\mathbf{j}.

Using \displaystyle \mathbf{r}=\mathbf{u}t+\frac{1}{2}\mathbf{a}{{t}^{\ 2}}+{{\mathbf{r}}_{0}} at \displaystyle \ \ t=10 gives

\displaystyle \mathbf{r}=(4\mathbf{i}– 8\mathbf{j}) \times 10+\frac{1}{2}(0\textrm{.}2\mathbf{i}+0\textrm{.}3\mathbf{j}) \times {{10}^{\ 2}}+6\mathbf{i}+2\mathbf{j}

\displaystyle \mathbf{r}=56\mathbf{i}– 63\mathbf{j}\ \ \text{m}{{\text{s}}^{-1}}