Final answer:
By convention in physics, an object moving downward is assigned a negative sign (-) to denote its direction of motion as being downward, which is considered the negative direction in a coordinate system. Option b is the correct answer.
Step-by-step explanation:
In physics, we often deal with objects in motion, whether it's moving upward, downward, or horizontally. The direction of an object's motion can be represented by a sign convention in problems involving gravity, acceleration, or any vector quantity. By conventional standards in physics, an object that is in motion and is moving downward is often assigned a negative sign (-). This is because the downward direction is typically considered the negative direction in a coordinate system where upwards is taken as positive.
The negative sign indicates the direction of the motion or force and is particularly important when working with equations of motion or when calculating work done by gravitational forces. For example, if an object is falling towards the Earth due to gravity, its acceleration due to gravity (commonly represented as 'g') is often assigned as -9.81 m/s2 because it is directed downward, towards the center of the Earth.
In summary, by convention, we denote the direction of an object moving downward with a negative sign (-), as it signifies motion in the negative y-axis direction for most coordinate systems used in physics.
The correct option is:
b. A negative sign (-)