Question

the figure below shows strobe photographs taken of a disk moving from left to right under different conditions. the time interval between images is constant. taking the direction to the right to be positive, describe the motion of the disk in each case. (a) for which case is the acceleration positive?

Explanation:

Step1: Recall acceleration concept

Acceleration is rate of change of velocity. Positive acceleration means velocity is increasing in positive - direction.

Step2: Analyze distance between dots

In strobe photographs, if the distance between successive dots (images of the disk) is increasing with time (since time - interval between images is constant), the velocity is increasing.

Step3: Identify the case

In the third case, the distance between the dots is increasing as the disk moves from left to right. So, the velocity of the disk is increasing in the positive (right - ward) direction, which means the acceleration is positive.

Answer:

The third case.