Solution 8.5b
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(New page: From part a) we have <math>\mathbf{v}=(80+t\ )\mathbf{i}+4t\ \mathbf{j}</math>. and <math>\mathbf{r}=(80t+\frac{1}{2}{t}^{\ 2}\ )\mathbf{i}+2{t}^{\ 2}\ \mathbf{j}</math> We see the ...)
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Revision as of 15:13, 14 April 2010
From part a) we have
\displaystyle \mathbf{v}=(80+t\ )\mathbf{i}+4t\ \mathbf{j}.
and
\displaystyle \mathbf{r}=(80t+\frac{1}{2}{t}^{\ 2}\ )\mathbf{i}+2{t}^{\ 2}\ \mathbf{j}
We see the height is
Thus the time when the aeroplane is at a height \displaystyle 50 \text{ m} .
We see the height is \displaystyle 2{t}^{\ 2} for any time \displaystyle t.
Thus the time when the aeroplane is at a height \displaystyle 50 \text{ m} is given by
\displaystyle 2{{t}^{\ 2}}=50
or
\displaystyle t=5\ \text{s}