What is speed?
rate of motion
rate and direction of motion
the direction of motion
the force of motion

rate of motion

Explanation:

Speed is the rate of motion, is the amount of movement that an object is experiencing in a certain amount of time, for scientific purposes speed is often calulated in meters per second, which is how many meters can an object move in just one secod.

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.

8 m/s because for him to get the same amount of energy as ray is putting out, bobby, who weighs half as much as ray, needs to run twice as fast.