00:01
So in this problem, we have a beam under some loading.
00:04
We want to first find what the reaction is, and we'll label that r.
00:09
And we also want to find the moments about point p and see if it obeys the principle of moments.
00:19
So to start, we want to find the reaction in a, the reaction at o.
00:24
So what is r? now, we'll need to pick a coordinate direction, and we'll say, as, is convention, we'll just start from x, start from o, an x direction, which we don't really need, but we can put down, and a y direction there.
00:45
And so we'll use the sum of forces is equal to zero, assuming that this is in static equilibrium, to find the unknown reaction.
00:54
So you see, there's a bunch of forces downward, and so the force up should balance them so that is not moving.
01:02
And we can start plugging in.
01:04
0 is equal to negative 10 newtons because it's downwards relative to the axis that we picked plus r because it's the other direction, minus 8, minus 3.
01:18
That's all our forces.
01:21
And it works out that the unknown reaction is 21 newtons.
01:31
So with that, we want to look at moments.
01:36
In part b, we want to see what the clockwise moments are and what is the total clockwise moments so of course we have clockwise and then the other direction will be anti -clockwise here i'll call it counterclockwise about point p so we'll start with 10 newton's and we see that the error is down and if we were to curve we would get something that matches clockwise so all the forces that are pointing down and are to the right of p which is all the forces will be counterclockwise.
02:22
So the 10, the 8, and the 3 are counterclockwise.
02:27
So 10, newton, 8, 3 newton, are, excuse me, clockwise, about.
02:43
And what is the total moment? we'll call that m.
02:52
And a moment is equal to a force and a distance.
02:59
And we need both of those for each.
03:03
So we look, we have the 10 newtons.
03:06
It's 4 minus 2.
03:08
So this works out to 2 meters.
03:14
And then we see for the 8 newtons, we have 4 plus 1, 5.
03:18
And for the 3 newtons, 4 plus 4 is all the right out at 8.
03:25
And so we can start plugging these in.
03:28
The 10 newtons and its distance, 2 meters.
03:33
And we add up all of these...