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Revision as of 16:54, 11 October 2010 (edit) Ian (Talk | contribs) (New page: The expression for the position vector<math>\mathbf{r}</math> has been obtained in part b),) ← Previous diff		Current revision (17:09, 11 October 2010) (edit) (undo) Ian (Talk | contribs)
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-	The expression for the position vector<math>\mathbf{r}</math> has been obtained in part b),	+	The expression for the velocity <math>\mathbf{v}</math> has been obtained in part a).
		+
		+	<math>\mathbf{v}=\left( 40 \right)\mathbf{i}+\left( -2t \right)\mathbf{j}</math>
		+
		+	If the aeroplane is travelling south this is in the negative <math>\mathbf{j}</math> direction.
		+
		+	If the aeroplane is travelling east this is in the positive <math>\mathbf{i}</math> direction.
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		+	Thus if the aeroplane is travelling south east the <math>\mathbf{i}</math> component of the velocity must equal the minus <math>\mathbf{j}</math> component of the velocity.
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		+	<math>\begin{align}
		+	& 40=-(-2t) \\
		+	& \\
		+	& t=20\text{ s} \\
		+	\end{align}</math>

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Current revision

The expression for the velocity \displaystyle \mathbf{v} has been obtained in part a).

\displaystyle \mathbf{v}=\left( 40 \right)\mathbf{i}+\left( -2t \right)\mathbf{j}

If the aeroplane is travelling south this is in the negative \displaystyle \mathbf{j} direction.

If the aeroplane is travelling east this is in the positive \displaystyle \mathbf{i} direction.

Thus if the aeroplane is travelling south east the \displaystyle \mathbf{i} component of the velocity must equal the minus \displaystyle \mathbf{j} component of the velocity.

\displaystyle \begin{align} & 40=-(-2t) \\ & \\ & t=20\text{ s} \\ \end{align}