00:01
Okay, we have this person who sees some water balloons falling past his window, and he notices that it takes them 0 .45 seconds to hit the ground after that passes window.
00:14
He's on the second floor, 10 meters above the sidewalk.
00:17
So we want to know how fast the balloons are going when they pass his window.
00:26
Okay, so we want to figure out how fast they're going when they pass his window.
00:33
So we're going to use this kinematic equation here.
00:41
Y final equals y initial plus the initial y velocity times time, plus one half acceleration in the y times squared.
00:52
Okay, what's called this point here, y equals zero.
01:04
And that will be our final position.
01:07
And we'll say positive y is up.
01:10
So y final equals zero.
01:12
Y initial is the 10 meters plus v0 times t and we're expecting v not to be negative with our coordinate system here right because we say up is positive so down is negative so we expect v not to be negative and then our acceleration is minus g um so if we plug all these things in we should get that v0 is going to be equal to 1 1 .g t squared minus y0 all that over t and that gives us a negative number so that's good so minus 20 .02 looks like meters per second okay so that's the speed of the water balloon as it passes that guy's window.
02:24
Okay...