E1t6 Retake Preap 2016

Acceleration is defined as the rate of change of velocity. Velocity is the rate at which an object's position changes, and acceleration measures how quickly the velocity is changing. It can be positive when an object is speeding up, negative when it is slowing down, or zero when it is maintaining a constant velocity. Therefore, option d is the correct answer as it accurately describes the definition of acceleration.

When the initial velocity of a car is positive and its acceleration is negative, it means that the car is moving in the positive direction but slowing down. This is because the acceleration is acting in the opposite direction to the initial velocity, causing the car to decelerate. As a result, the speed of the car will decrease over time.

The object travels the same distance of 8 m in each second of travel, which means its velocity remains constant. Since acceleration is defined as the rate of change of velocity, and the velocity is not changing, the acceleration is 0 m/s^2.

As the car travels around a circular track at increasing speed, its acceleration is not zero. Acceleration is the rate at which velocity changes, and since the car is increasing its speed, there is a change in velocity and therefore acceleration is not zero. Similarly, the velocity is also not zero because the car is moving and increasing its speed. Therefore, the correct answer is none of the above.

When a car travels around a circular track at a constant speed, its velocity is zero. This is because velocity is a vector quantity that includes both speed and direction. In this case, although the car is moving at a constant speed, its direction is constantly changing as it moves around the circular track. As a result, the car's velocity is constantly changing, and at any given point on the track, it is zero.