00:01
Alright, for this problem, we had these questions.
00:05
We have a car, and it is trying to stop.
00:09
And we know the friction is 25 % of its weight, and it has mass of 1750 kilograms, and its initial velocity before hitting the brakes is 110 kilometers per hour.
00:18
We want to know what is the acceleration of the car.
00:21
So, first off, i need to make a note of some things.
00:28
All right.
00:29
The car's weight is equal to this mass, times the acceleration constant of gravity which is equal to i'm going to cheat and scroll down to my scratchwork surround the news calculator okay looks like when i did that i got 17 ,150 newtons oh these equations here in gold these are just common equations concerning kinematic motion that we that have been given to us in prior chapters and the top one is distance and the bottom one is the same question but modified where if we for t, we could solve for t by itself and plug it in to this equation and then we would get this equation down here as a result.
01:25
Notice how the equation on the bottom doesn't have a t in it.
01:28
That'll become important later.
01:30
So that's what those are.
01:33
Anyway, save the carb weight.
01:35
We know that the friction is 25 % of the car's weight.
01:38
So the friction force is equal to 0 .25 times 17 -150.
01:52
Newton's and that's going to give us, again, i'm going to cheat and use my scratch work, because then i don't have to re -type in a calculator.
02:01
4287 .5.
02:06
All right, so we have a friction force.
02:08
All right, now, the acceleration, remember that we can use the equation from newton's and second law motion.
02:14
You know the sum of the forces on x need equal the mass.
02:20
Well, the forces in the x direction.
02:23
People for the mass times the acceleration.
02:26
X right in the x direction.
02:28
The friction force we just said is this 4287 .5.
02:35
That's the only force we have acting on this car, so it's stopping, is this friction.
02:44
And then we're dividing it by its mass.
02:47
So this is newton's.
02:49
Oh my goodness, so hard to write.
02:51
Newton's.
02:52
Then we divide by its mass, which is 1750 kilograms.
03:00
If we divide kilograms and newtons, we get a meter per second squared.
03:04
And this gets us a whole, i believe it's, use my notes again, okay, gets me a whole 2 .45 meters per second squared.
03:17
Okay, so we have, so this is equal to the acceleration...