Final answer:
A car is accelerating when there is a change in its velocity, either through a change in speed or direction. Scenario (c) where the car goes around a circular track at a steady speed is an example of acceleration due to a changing direction, while scenario (d) provides a clear case of acceleration by increasing speed.
Step-by-step explanation:
A car is considered to be accelerating when there is a change in its velocity, which can be due either to a change in speed or direction, or both. In this case:
(a) Traveling on a straight, flat road at 50 miles per hour does not represent acceleration if the speed is constant, because there is no change in speed or direction.
(b) Traveling on a straight uphill road at 30 miles per hour could represent acceleration if the car is increasing its speed up the hill, but not if the speed is constant.
(c) Going around a circular track at a steady 100 miles per hour represents acceleration because, even though the speed is constant, the direction of velocity is changing due to the circular path.
(d) Drive the car at exactly 50 mph and then apply the accelerator until it reaches the speed of 60 mph and record the time it takes is a situation where the car is definitely accelerating, as there is an increase in speed.
The correct response to the original question depends on the context given in each scenario, but generally, a car is accelerating when its velocity changes, which includes scenarios (b) if the speed is increasing, and (c) because the direction is changing.