when is a velocity is zero and acceleration nonzero?
Not necessarily; it can be accelerating as it reverses direction.
..or it can be completely stationary and not accelerate at all.
...or the two directions might be at right angles. I.e. the object might be accelerating in the North direction, but have zero velocity in the Westerly direction.
When is velocity zero and acceleration nonzero? To understand this concept, we need to have a basic understanding of velocity and acceleration.
Velocity is a measure of how fast an object is moving in a given direction. It is a vector quantity, which means it has both magnitude (speed) and direction. Acceleration, on the other hand, measures the rate of change of velocity. It also a vector quantity.
In most cases, when velocity is zero, it means that an object is momentarily at rest, not moving. However, there are situations where an object's velocity can be zero while its acceleration is nonzero. Here are a couple of examples:
1. Changing direction: Imagine a car traveling along a straight road. As it approaches a junction, the driver quickly turns the steering wheel, making the car change direction. At the moment the car changes direction, its velocity becomes zero because it momentarily stops moving in a straight line. However, since the car is accelerating due to the change in direction, its acceleration is nonzero.
2. Projectile motion: Consider a ball thrown directly upward. At the highest point of its trajectory, the ball momentarily comes to a stop before it starts to fall back down due to the acceleration due to gravity. Therefore, at the highest point, the ball's velocity is zero, but its acceleration is nonzero (equal to the acceleration due to gravity, which is typically denoted as "g").
To summarize, velocity can be zero while acceleration is nonzero in cases where the object is changing direction or reaching the extreme points of its motion, such as the highest point in projectile motion.