A new model of sports car is being tested on a long, straight, horizontal roadway. The car is
initially at rest at position x = 0. At time t = 0, the car begins to speed up with a constant
acceleration of 6 m/s 2 . The car has this constant acceleration for 5 seconds.
(a) At time t = 5 seconds, the car is at position x = D. Calculate the value of D.

(b) On the grid below, draw the velocity of the car as a function of time for the first five
seconds of the car’s motion.

At time t = 10 seconds, the car is at position x = 2D. Three students each suggest what motion
the car could have had between t = 5 s and t = 10 s that would account for this fact.
___ Student A: The car slows down with the same magnitude acceleration that it had during the
first 5 seconds.
___ Student B: The car continues to speed up with the same acceleration that it had during the
first 5 seconds.
___ Student C: The car ceases to accelerate and simply has a constant velocity between t = 5 s
and t = 10 s.
(c) Mark the blank next to the student whose suggestion correctly explains why the car is at
position x = 2D at time t = 10 seconds. On the grid in part (b), complete the graph by
drawing the car’s velocity during the interval t = 5 s to t = 10 s consistent with the motion
suggested by the student that you marked.
(d) Use your graph to explain your selection of student.