To solve this question:

Problem Analysis:

The fly is sitting on the tip of the second hand of a clock. As the second hand moves from the "12" position to the "9" position (a quarter-circle clockwise), the fly undergoes circular motion. The average acceleration depends on the change in velocity during this time interval.

Key Concepts:

1. Initial Velocity ($v_i$): At "12," the velocity vector of the fly is tangent to the circle and points horizontally to the right (positive x-direction).

2. Final Velocity ($v_f$): At "9," the velocity vector of the fly is tangent to the circle and points vertically downward (negative y-direction).

3. Change in Velocity ($\Delta v = v_f - v_i$): To find the direction of the average acceleration, consider the vector subtraction $v_f - v_i$. This subtraction effectively points from the tip of $v_i$ to the tip of $v_f$ on a vector diagram.

4. Direction of Average Acceleration: The vector $\Delta v$ points diagonally inward toward the center of the clock (since it is the average of the velocity change over a quarter-circle path). Specifically, the direction is toward the center of the clock face.

Correct Answer:

The direction of the average acceleration is D).

Do you want a detailed vector breakdown or explanation of average acceleration? Here are some related questions to explore:

1. Why does the acceleration point toward the center during circular motion?
2. What would the velocity vectors look like if the fly traveled from "12" to "6" instead?
3. How does uniform circular motion differ from non-uniform circular motion in terms of acceleration?
4. What happens to the average acceleration if the fly completes a full circle?
5. How is centripetal acceleration calculated, and why is it always directed inward?

Tip: In circular motion, the average acceleration vector often points toward the center, especially when the path covers symmetrical arcs (like quarter-circles).