It cannot have negative velocity, it can have negative acceleration.
If you have a Displacement - time graph, the velocity at a certain point equals displacement over time, displacement is a vector quantity thus is affected by direction so when it has a negative value the velocity has a negative value. and if your still thinking about it, check out this thought: "negative velocity is positive velocity in the other direction"
No, momentum can not have a negative velocity. Velocity is the rate of motion of a body from one position to another position in a particular direction. Bodies traveling in opposite directions may appear to have a negative velocity in relationship to each other but any amount of velocity is positive.
Downward velocity is considered a negative. This is a true statement.
Observe that the object below moves in the negativedirection with a changing velocity. An object which moves in the negative direction has a negative velocity. If the object is speeding up then its acceleration vector is directed in the same direction as its motion (in this case, a negative acceleration).
Deceleration. Negative acceleration = Velocity is decreasing by time. Positive acceleration = Velocity is increasing by time. Zero acceleration = Velocity is the same by time.
It depends on what information you have. Also, velocity can be negative - it just means that the object is travelling in the direction opposite to the positive direction for the velocity vector.
Negative
Acceleration is negative if velocity is decreasing with time. Since velocity is a vector this can occur in one of two ways: 1) you are slowing down in the direction of motion and the velocity in that direction is defined as positive (this is what we usually mean by negative acceleration) 2) you are speeding up in the direction of motion and the velocity in that direction is defined as negative. An example of this is an object launched into the air which immediately starts to decelerate in it's upward velocity, reaches it's highest velocity, and then begins accelerating towards the ground. If we call the velocity upward a positive velocity, then when it starts falling, it has negative velocity. Note that acceleration (due to gravity) is negative the whole time.
If you are decreasing velocity, you are undergoing negative acceleration.
A negative slope on a velocity-time graph indicates a decreasing velocity over time, which means the object is slowing down. As time increases, the velocity decreases.
Deceleration (or negative acceleration).