Question

A car travels along a road and its odometer readings are plotted against time in Fig. $1-8$. Find the instantaneous speed of the car at points $A$ and $B$. What is the car's average speed? Because the speed is given by the slope $\Delta l / \Delta t$ of the tangent line, we take a tangent to the curve at point $A$. The tangent line is the curve itself in this case, since it's a straight line. For the triangle shown near $A$, we have $$ \frac{\Delta l}{\Delta t}=\frac{4.0 \mathrm{~m}}{8.0 \mathrm{~s}}=0.50 \mathrm{~m} / \mathrm{s} $$ This is the speed at point $A$ and it's also the speed at point $B$ and at every other point on the straight-line graph. It follows that $v=0.50 \mathrm{~m} / \mathrm{s}=v_{a v}$

          A car travels along a road and its odometer readings are plotted against time in Fig. $1-8$. Find the instantaneous speed of the car at points $A$ and $B$. What is the car's average speed?
Because the speed is given by the slope $\Delta l / \Delta t$ of the tangent line, we take a tangent to the curve at point $A$. The tangent line is the curve itself in this case, since it's a straight line. For the triangle shown near $A$, we have
$$
\frac{\Delta l}{\Delta t}=\frac{4.0 \mathrm{~m}}{8.0 \mathrm{~s}}=0.50 \mathrm{~m} / \mathrm{s}
$$
This is the speed at point $A$ and it's also the speed at point $B$ and at every other point on the straight-line graph. It follows that $v=0.50 \mathrm{~m} / \mathrm{s}=v_{a v}$

Added by Aaron C.

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