Motion in one Dimension 3 - acceleration direction
Motion in one Dimension 3 - acceleration
Figure3-1
Again we came back to the above situation.
Don't you have any questions about it?
No? Nothing?
Then I will ask a question to you.
The driver really can come to his home safely?
Will he see his wife and children and then take dinner with them?
What do you think about it?
No. With above physical conditions he never enter the house safely.
Because before enter home, the car need to be stopped. What should he do?
Yes. He have to step break pedal to stop moving.
Today let's look into the motion in break on.
I will re-arrange the car's situations like below.
Figure3-2
He stepped break pedal softly and continuously. So the speed became smaller gradually. In other words, the magnitude of velocity is going down gradually until it's stopped.
But the direction of Velocity is (+) direction.
Anyway the velocity is changing now.
We've checked the definition of acceleration.
Let's set the magnitude of velocity after t2 second.
And the magnitude of velocity after t1 second.
t2: the time after t second, t1: initial time.
then t2 > t1
and v2 < v1
so v2 - v1 < 0, at once, minus.
Therefore the acceleration a has minus direction.
It means the direction of velocity and acceleration are opposite each other.
We can conclude then if acceleration and velocity are opposite each other, the speed goes down continuously until the car is stopped. At the moment, the speed v2 will be 0.
I will set the car's acceleration by (-) 1 (m/s2).
It means the speed will be reduced 1 m/s per 1 second. So after 10 second the speed will be 20 m/s - 10 m/s = 10 m/s.
Let's check the physical quantities of the car including the driver.
comment
And let's apply motion formula for constant acceleration in one dimension.
I will rewrite again.
formula
After 20 second the speed will be 0. We can check it by 1st formula.
V2 = 20 + (-1)*20 = 0 (m/s)
It means after 20 second the car will be stopped.
Then where the car will be located after 20 second?
Let's use 2nd formula.
S = 20*20 + (1/2)*(-1)*(20)2 = 400 - 200 = 200 (m)
Homework 3-1 induce above conclusion, S = 200 (m) through 3rd formula.
So the car moves 200(m) distance toward east direction from (-)10 (km) position.
Then what will be the displacement at that time? Below is expressing the car's displacement.
displacement
What can we conclude then? He stepped break pedal so early. He can not arrive at home yet.
Then,
HW 3-2 When and where should he step the break pedal. Write down all solving process.
Figure3-1
Again we came back to the above situation.
Don't you have any questions about it?
No? Nothing?
Then I will ask a question to you.
The driver really can come to his home safely?
Will he see his wife and children and then take dinner with them?
What do you think about it?
No. With above physical conditions he never enter the house safely.
Because before enter home, the car need to be stopped. What should he do?
Yes. He have to step break pedal to stop moving.
Today let's look into the motion in break on.
I will re-arrange the car's situations like below.
Figure3-2
He stepped break pedal softly and continuously. So the speed became smaller gradually. In other words, the magnitude of velocity is going down gradually until it's stopped.
But the direction of Velocity is (+) direction.
Anyway the velocity is changing now.
We've checked the definition of acceleration.
Let's set the magnitude of velocity after t2 second.
And the magnitude of velocity after t1 second.
t2: the time after t second, t1: initial time.
then t2 > t1
and v2 < v1
so v2 - v1 < 0, at once, minus.
Therefore the acceleration a has minus direction.
It means the direction of velocity and acceleration are opposite each other.
We can conclude then if acceleration and velocity are opposite each other, the speed goes down continuously until the car is stopped. At the moment, the speed v2 will be 0.
I will set the car's acceleration by (-) 1 (m/s2).
It means the speed will be reduced 1 m/s per 1 second. So after 10 second the speed will be 20 m/s - 10 m/s = 10 m/s.
Let's check the physical quantities of the car including the driver.
comment
And let's apply motion formula for constant acceleration in one dimension.
I will rewrite again.
formula
After 20 second the speed will be 0. We can check it by 1st formula.
V2 = 20 + (-1)*20 = 0 (m/s)
It means after 20 second the car will be stopped.
Then where the car will be located after 20 second?
Let's use 2nd formula.
S = 20*20 + (1/2)*(-1)*(20)2 = 400 - 200 = 200 (m)
Homework 3-1 induce above conclusion, S = 200 (m) through 3rd formula.
So the car moves 200(m) distance toward east direction from (-)10 (km) position.
Then what will be the displacement at that time? Below is expressing the car's displacement.
displacement
Then,
HW 3-2 When and where should he step the break pedal. Write down all solving process.
