### The motion diagram shown in the figure represents a pendulum released from rest at an angle of from the vertical. The dots in the motion diagram (Figure 1) represent the positions of the pendulum bob at eleven moments separated by equal time intervals. The green arrows represent the average velocity between adjacent dots. Also given is a “compass rose” in which directions are labeled with the letters of the alphabet.

A) What is the direction of the acceleration of the object at moment 5?

B) What is the direction of the acceleration of the object at moments 0 and 10?

SOLUTION:

**PART A:**

**Answer: A**

The acceleration of the object at moment 5 is the acceleration found from the change in velocity between moments 4 and 5 and moments 5 and 6.

Acceleration is defined as the change in *velocity* per unit time. Mathematically,

Since velocity is a vector, acceleration is a vector that points in the direction of the *change* in the velocity.

**Part B:**

**Answer: D,F**