00:01
Okay, so for this one, we're given an initial velocity of 7 .47 meters per second.
00:08
The elevator is brought to rest, so the final is zero.
00:13
We want to know the acceleration, and the distance is 9 meters.
00:23
Okay, so we're going to use the equation vf squared is equal to vi squared plus 2a delta x, and vf is zero.
00:33
V .i is 7 .47, and delta x is 9.
00:42
Okay, so let's see here.
00:44
Throughout the square.
00:46
So this is a zero.
00:47
We're going to get negative 7 .47 squared.
00:50
Let me actually type that in.
00:53
So this is negative 55 .8 is equal to 18a, and then dividing by 18 on both sides, gives us 3 .1.
01:11
So negative 3 .1, meters per second squared.
01:15
That's going to be our acceleration.
01:18
Okay, so ultimately we want to figure out for part a here, the tension.
01:22
So let's draw a force diagram for this.
01:24
We're going to have gravity acting on this object.
01:28
So force of gravity is going to be mg, which would be 3 ,300 mass times 9 .8.
01:36
So 32 ,340 is the force of gravity.
01:41
Tension is going to be, it's moving.
01:45
Upward but slowing down.
01:47
So it's a downward acceleration.
01:48
That's where that negative is coming coming from here.
01:52
So in other words, tent is going to be less than gravity.
01:56
And we can use newton's laws to calculate this.
01:59
So net force is equal to mass times acceleration.
02:04
The net force is going to be tension minus gravity...