Final answer:
In physics, the reference point is generally assigned a value of zero to denote an object's position on a straight line. Speed is calculated by dividing distance traveled by time elapsed. These concepts are essential in understanding and describing motion in physics.
Step-by-step explanation:
In the context of an object's position on a straight line, a reference point is most often given a value of zero. This reference point is a chosen location from which distances and displacements are measured. Option b and d is correct answer.
Speed is calculated by the formula: Speed = Distance / Time. It is the rate at which an object covers distance and is a scalar quantity, meaning it only has magnitude and no direction. Therefore, to find the speed, we divide the total distance traveled by the elapsed time the object has been moving.
To summarize, displacement could also be zero when the object returns to its initial position, resulting in no change in location. Distance, on the other hand, accounts for the total ground covered and can never be negative. Both concepts significantly contribute to understanding an object's motion on a straight line.