1. (40 points) A driver is traveling on a straight country road at constant velo
ID: 1578837 • Letter: 1
Question
1. (40 points) A driver is traveling on a straight country road at constant velocity Vi. She spots a spare tire in the middle of the road at initial time t1-0. Her reaction time is 2.40 seconds. Thus, after a time period of 2.40 seconds the driver applies the brakes and starts to slow down. After putting on the brakes, the car decelerates with constant acceleration-4.92 m/s until coming to rest at time ts. At time t2, the displacement from the initial position is 24.5 m. A diagram of the velocity vs ime t for the motion is shown below v(m/s) t (sl (a) (20 points) What is the average velocity for the motion between tz and ts? (b) (20 points) What is the average velocity for the entire motion between ti and ts?Explanation / Answer
during reaction time.
d = v t
24.5 = 2.40 v
v = 10.21 m/s
after that vf^2 - vi^2 = 2 a d
0 - 10.21^2 = 2(-4.92) d2
d2 = 10.6 m
vf = vi + a t
0 = 10.21 - 4.92(t3 - t2)
t3 - 2.40 = 2.075
t3 = 4.475 sec
(A) average velociyty = displacement / time
= ( 10.6) / (2.075)
= 5.1 m/s
(B) average velocity =(10.6 + 24.5) / 4.475
= 7.84 m/s
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