Speed of a car The accompanying figure shows the time-todistance graph for a sports car accelerating from a standstill.
GRAPH CANT COPY
a. Estimate the slopes of secants $P Q_{1}, P Q_{2}, P Q_{3},$ and $P Q_{4}$ arranging them in order in a table like the one in Figure 2.6 What are the appropriate units for these slopes?
b. Then estimate the car's speed at time $t=20 \mathrm{sec}$