I am in lecture 18, can anyone help me understand the concept and how the formula for How fast is the arrow traveling, is calculated this is also present in the PPT, the first page of formula?

Question

e.mccormick · Answer

I do not know what PPT you are talking about off hand.  I'll have to look it all up... but, what you are discussing is instant speed, this can be presented as a calculus question or an algebra one depending on what you know. 

Lets say I look at how long it took an object to travel 10 feet by filming it. That gives me the average speed over those 10 feet. But I want the exact speed at the center, not the average speed. So I cut off the forst and last few feet and now I havd the average over 4 feet... on and on I shrink it more and more until I am at effectivly no time and have the average at no time change, so the speed it is going at that instant.

This idea is expressed in calculus as how when rate of time approches 0 you can look at both the acceleration and the speed for a particular moment.

Now, what if I knew how fast it was going at the start and I was told how rapidly it was slowing down? Well, then I could just buld a formula for the initial speed minus the product of the time and deceleration. This reduces it to an algebra problem because more is given and less is unknown.