"A toy airplane flies clockwise at a constant speed in a horizontal circle of radius 8.0 meters. The magnitude of the acceleration of the airplane is 25 meters per second squared. The diagram shows the path of the airplane as it travels around the circle.

State the direction of the velocity of the airplane at the instant the acceleration of the airplane is southward"

The airplane is moving by uniform circular motion - this means that there is a centripetal force that "pulls" the airplane towards the centre of the circle. The acceleration, which is called centripetal acceleration, has the same direction of the force, so it is directed towards the centre of the circle at any point of the motion.

Therefore, the acceleration of the airplane is southward when the airplane is on the top position (north).

What about the velocity? In a circular motion, the velocity of the object is always tangential to the circle, in the direction of the motion. Therefore, when the airplane is at the top position (north), the velocity of the airplane is eastward.