Negative work follows when the force has a component opposite or against the displacement. Negative work removes or dissipates energy from the system. Two examples: In pulling a box of books along a rough floor at constant velocity, I do positive work on the box, that is I put energy into the system.

A scalar quantity has magnitude or size, examples: distance, speed. Vector quantities have both magnitude and direction, examples: force, velocity and field strength. Speed here does not have any specific direction and have only magnitude so is a scalar quantity.

Angular momentum is a vector quantity that represents the product of a body’s rotational inertia and rotational velocity about a particular axis. The angular momentum is the product of the moment of inertia and the angular velocity around an axis.

Velocity as a Vector Quantity Because the person always returns to the original position, the motion would never result in a change in position. Since velocity is defined as the rate at which the position changes, this motion results in zero velocity. As such, velocity is direction aware.

Constant velocity means that the object in motion is moving in a straight line at a constant speed. This tells us in which direction the object moves.

If a body is moving with constant velocity, acceleration is zero. So net force acting on it will be also zero. But the body has energy due to its constant motion. So even if the body is moving with constant velocity, it can impart its momentum to other body.

When an object is speeding up, the acceleration is in the same direction as the velocity. Thus, this object has a positive acceleration. In Example B, the object is moving in the negative direction (i.e., has a negative velocity) and is slowing down.

Explanation: Speed increases when velocity and acceleration have the same sign. In section A, the velocity is positive because it’s above the x axis and the slope is positive, meaning that the acceleration is positive.