00:01
In this problem, we have a lot of different speeds, and we have a time of flight for each thing.
00:09
So what we've got to do is they want us to verify manually the values we obtained for the time of flight.
00:17
So if our initial speed is five, so we're going to assume here that everything is going to the right.
00:30
And so it says our initial height is equal to 12 meters.
00:39
So we can say that the original velocity and the y direction is equal to zero meters per second.
00:51
And if we know that the change in y is equal to 12 meters, and gravity is equal to 12 meters, to negative 9 .8 meters per second squared.
01:06
And if we have a cliff and this thing is falling, that 12 meters, we're going to make it negative because we're going to say that in the down direction, everything is negative, and then the up direction, everything is positive.
01:20
So let's use our kinematics equation to figure out how long this thing is in the air.
01:28
So first thing we'll do is we'll just say, delta y, so that's the change in height, is equal to the original speed in the y direction times time, minus one half of gravity times times squared.
01:47
So if we do that, we notice that vo is zero, so this term crosses off.
01:53
We've got negative 12 meters, and so that's equal to, and this we're going to make plus, equal to one half of negative 9 .8 times our time squared.
02:07
So now we need to solve for this time.
02:09
We're going to say that time is equal to the square root and the negatives become positive now.
02:17
So now we have 2 times 12, which is 24, and we're going to divide that by 9 .8.
02:24
If we use our calculator, we can take 24 divided by 9 .8...