00:01
We're told a ball is thrown in the air with velocity of 40 feet per second, and its height can be given by the equation y is equal to 40t minus 16t squared.
00:12
We want to find a velocity when time is equal to 2.
00:17
Now, the thing we'll need to recall from physics is that velocity is equal to the derivative or the rate of change of our displacement.
00:31
So we normally write this as like delta y or delta t.
00:36
But in this case, what we're really finding is the derivative of this function at 2.
00:44
So if we were to call this function f of t, we're wanting to find what is f prime of 2.
00:52
So what we would do for that is the limit as t approaches 2 of f of t minus f of 2, all over t minus t.
01:06
Now we need to figure out what f of 2 is.
01:10
So let's see.
01:13
F of 2 is going to be, so it would be 80 minus 16 times 2 squared, which is 4, which is going to be 64.
01:34
And then subtracting those should give us 16...