Section 2.2 Instantaneous Velocity 2.7 . CALC A car is stopped at a traffic light. It then travels along a straight road so that its distance from the light is given by x(1) = bt2 - ct, where b = 2.40 m/s' and c = 0.120 m/s'. (a) Calculate the average velocity of the car for the time interval t = 0 to / = 10.0 s. (b) Calculate the instantaneous velocity of the car at 1 = 0, t = 5.0 s, and / = 10.0 s. (c) How long after starting from rest is the car again at rest? 2.8 . CALC A bird is flying due east. Its distance from a tall build- ing is given by x(t) = 28.0 m + (12.4 m/s)t - (0.0450 m/s3)+3. What is the instantaneous velocity of the bird when ? = 8.00 s? 2.9 .. A ball moves in a straight line (the x-axis). The graph in Fig. E2.9 shows this ball's velocity as a function of time. (a) What are the ball's average speed and average velocity during the first 3.0 s? (b) Suppose that the ball moved in such a way that the graph seg- ment after 2.0 s was -3.0 m/s instead of +3.0 m/s. Find the ball's average speed and average velocity in this case. Figure E2.9 Ux (m/s) 3.0 2.0 1.0 1 (s) o 1.0 2.0 3.0