00:01
Example i'm going to be looking at our kinematics equations for a motion under constant acceleration and we're going to be looking at an example of a toy rocket.
00:09
So we have a toy rocket launched from ground level and it's going to travel upwards to a height of 1 .2 kilometers or 1 ,200 meters.
00:25
At this point its rocket fuel is depleted and it is no longer being propelled.
00:32
And at this point, it has a velocity of 329 meters per second.
00:38
Okay, so we know we start from rest.
00:40
Fee initial equals zero.
00:42
My final velocity after the rocket runs out of fuel, is 329 meters per second.
00:51
And the first thing i want to do is find the rate at which this rocket was accelerating from the time it left the ground to the time it reaches the high.
01:00
Height of 1 .2 kilometers and runs out of fuel.
01:03
So the equation i'm going to use is v.
01:07
Final squared equals v initial squared plus 2a, delta d, where that's my final velocity.
01:20
My initial velocity, 2 is 2.
01:22
Acceleration is what we're looking for, and delta d is the change in distance.
01:27
So in this case, it'll be our change in height.
01:30
I've started from rest, as i've said, so this term drops out.
01:35
And i have a just equals the final squared over 2 delta d.
01:45
And in this case we go from initial height of zero to our final height of 1 .2 kilometers.
01:52
And that gives me an acceleration of a equals 45 .1 meters per second squared or about 4g.
02:07
All right.
02:08
Now the next question asks, what's the rocket's acceleration after the engine has burned out? well, the only force we have acting on it is the force due to gravity...