00:05
A truck's distance while slowing down is 40 meters.
00:12
The time to slow down is 8 .5 seconds.
00:21
It's 40 meters.
00:23
I don't know what my problem is up there.
00:31
And the final velocity is 2 .8 meters per second.
00:41
What's the initial speed? well, v final.
00:52
Squared is v -initial squared minus 2a -d, but also v -final equals v -initial minus a t.
01:16
So solving the second equation for a gives me over t.
01:29
No, that's not right.
01:39
A is going to be v -initial minus v final over t.
01:47
So substituting that into the first equation.
02:09
All right.
02:12
Now i'm going to graph that in desmos.
02:19
And how i'm going to do that is i'm going to subtract vf squared on both sides.
02:26
That's going to give me zero over here.
02:31
And now everywhere that i see v sub zero, which is two places, i'm just going to write x.
02:38
So, in desmos, declare my variables first.
02:47
D equals 40, t equals 8 .5, b final is 2 .8.
03:00
Are you right, 2 .8? it seems right.
03:05
Yeah, it is.
03:08
Okay.
03:10
So i'm going to write v0 squared, which is going to be x squared, minus 2, x minus v final over t times d minus v final squared.
03:39
So i've graphed it, and now i'm going to look for the x intercept.
03:46
There is an x intercept at the initial.
03:54
I guess i'm just going to go with the first x intercept.
03:58
Of 2 .8 seconds.
04:07
Or wait a minute, 2 .8, that would be v0, so that would be meters per second.
04:17
29, and that's wrong.
04:24
So let's think about this again, because it says it's supposed to be 6 .61.
04:31
So 40 meters in 8 .5 seconds, final velocity is 2 .8.
04:39
That seems questionable to me.
04:43
So let me go into the book.
04:49
That's right...