# Problem 2-99 - v-t graph - Part 9 - (b)

Two cars, A and B, are stopped for a red light beside each other at an intersection. The light turns green and the cars accelerate. Their velocity time graphs are shown in Figure 2 44. (The positive direction is "forward.")

(a) At what time(s) do A and B have the same velocity?
(b) When does B overtake A? (Hint: Their displacements must be equal at that time and displacement can be found from a velocity time graph.)
(c) How far have the cars traveled when B overtakes A?

Accumulated Solution

The velocities are equal at $\mathrm{t = 45\; s}$

$\mathrm{d_{A,60} = (1/2)(15\;m/s)(30\;s) + (15\;m/s)(30\;s) = 675\; m}$

$\mathrm{d_{B,60} = (1/2)(20\;m/s)(60\;s) = 600\; m}$

$\mathrm{d_{A,60} - d_{B,60} = 75 \;m}$

$\mathrm{v_{B,A}= 5\; m/s}$

No. Check the units.

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