Hey, guys. Let's check out this problem. We've got a 100 kilogram load of bricks that's being lowered on a cable. So basically, I've got this load of bricks that's 100 kilograms. I'm just going to draw it as a box. It's being suspended by a cable, but that cable is actually lowering this load of bricks. So we know the velocity here is equal to 5 meters per second. And eventually, what happens is over some period of 2 seconds, it's going to slow to a stop, which means that there are some time period here, I'm going to call this t, which equals 2 seconds. Eventually, this load of bricks will come to a stop, which means the velocity is going to equal 0. So what I'm going to do is I'm going to call this the initial velocity, which is my 5 meters per second. The final velocity is 0. What I want to do is I want to figure out what is the tension in the cable so that this load of bricks actually comes to a stop. Right? So the first thing we have to do is we're going to draw a free-body diagram. So I'm going to do that over here. This is going to be my free-body diagram. So basically, I'm going to have this little dot like this. I have the weight force, the weight force is going to be downwards. This is my W=mg, and that also got a tension force like this. And this is basically what I'm trying to solve for. Alright? So if I'm basically trying to solve for this tension force, again, we look at any other forces. There's no applied forces because you don't have anything pushing or pulling. You also don't have a normal or friction because this thing is in the air. Right? So our free-body diagram is pretty straightforward. It's only these two forces, and now we're getting into our F=ma. So if our F=ma, we have to expand our forces. We need to know the direction of positive. So we're just going to choose the upward direction to be positive. Alright? So now we got our forces. We've got tension that's upwards and then our mg is downwards. So our equation becomes t-mg=ma. Now we want to figure out what this tension is, so I need to figure out everything else in the problem. I have to know mass. I have to know g. I have to know mass and the acceleration. But do we actually know the acceleration? We actually don't. If you look at the problem, all we're told is that this thing is going downwards at 5 meters per second, and then over 2 seconds, it stops. That doesn't tell us what the acceleration is. And so we're kind of stuck here. How do we figure this out if we don't know the acceleration? Well, remember what happens is that if you ever get stuck solving for a, you can always try to solve it using a motion equation, and that's exactly what we're going to do here. So if we want to figure out the acceleration, I'm going to need to write out my 5 kinematics variables. Right? I'm given stuff like initial velocity, final velocity, time So these are all motion variables So I need to know the delta y, this is my v naught, v, a, and t I just need to know 3 out of 5 variables and then I can pick an equation to solve. So I don't know what my delta y is. I don't know the distance that this thing is stopping through, but I do know my initial velocity is 5. Is it 5, though, or is it negative 5? Remember what happens is that you the, direction of velocities and accelerations depend on which direction you choose to be positive. We chose up to be positive, so this v naught actually points down even though we write it as a positive in the diagram. When we're doing math, we actually have to write it with the correct sign. So it's negative 5. The final velocity is 0. The acceleration is actually what we're trying to find here. And we know the time is equal to 2 seconds. So fortunately, And that equation is going to be the simplest one, number 1, which says that the initial, sorry, final velocity is going to be initial velocity plus a times t. So we can use this to find a. So our final velocity is 0. Initial velocity is negative 5 plus, and then we've got a times 2. So if you bring this negative 5 over to the other side, it becomes positive So 5 equals 2a and so your acceleration is going to be 2.5 meters per second squared. So let's talk about the sign. Remember that when you solve for the acceleration, as long as you've plugged in everything correctly, you should get the correct sign, and it should indicate the acceleration's direction. So which means which means that we got a positive number. That just means that we got an upward acceleration. So the upward acceleration is 2.5. This should make some sense. Right? So if the load of bricks is going downwards with 5 meters per second, in order for it to come to a stop, the acceleration has to point upwards. Right? So we got an acceleration of 2.5. Now we can just plug this number back into our F=ma and then solve for the tension. So what happens is we're going to move this mg to the other side and tension becomes mg+ma. You could also just move you can merge those into under parentheses, that's up to you. So the tension is equal to, and now we just plug everything in, 100 times 9.8 plus 100 times the acceleration which is 2.5, and we plug it in as a positive, remember. So if you work this out what you're going to get is 1230 Newtons. So we looked through our answer choices 1230, and that's going to be answer choice a. So we've got our attention is 1230. This should make some sense that we got a 1230 because in order for the acceleration to be up, right, which we want for the load of bricks to slow to a stop, it has to be bigger than your weight force which is 980. So even though the load of bricks is moving downwards, the tension force still has to be bigger to produce an upward acceleration so that the load of bricks stops. Alright? So that's it for this one, guys.