Suppose that you can lift no more than 650 N (around 150 lb) unaided.

(a) How much can you lift using a 1.4-m-long wheelbarrow that weighs 80.0 N and whose center of gravity is 0.50 m from the center of the wheel (Fig. E11.16)? The cen-ter of gravity of the load car-ried in the wheelbarrow is also 0.50 m from the center of the wheel. (b) Where does the force come from to enable you to lift more than 650 N using the wheelbarrow?

Video transcript

Hey everyone in this problem, we have a female worker in the workplace with a safe limit to lift objects weighing 116 units or 16 kg. The worker can lift weights greater than 160 newtons using a trolley, so we can consider this 1.5 m long trolley weighing newtons and the center of gravity located 6.6 m from the axle. We're going to assume the load center of mass is located 0.6 m from the axle and were asked what is the source of the force that enables a worker to lift more weight using the trolley. So this question is asking us some information about a force. So let's go ahead and draw the forces that we have acting on this diagram. So we have a force here acting upwards when the female worker lifts the trolley. So we're going to say that that's F. L. Okay, The force related to lifting the trolley, we have a force acting on the wheel, we'll call it F. W. That's acting on the wheel from the ground, we have the weight of the trolley acting downwards, and we also have the weight of the load acting downwards. Now we have these forces downwards and we remember that we always have to also have an opposing force, the normal force pointing upwards. Alright, so we want to figure out what is the source of the force that enables a worker to lift more weight. So what that means is what is the source of the force that enables the worker that enables this force F. L. That amount that they're lifting to be greater than the weight of the load. So, let's look at the sum of the forces in the Y direction, we know an equilibrium, This is going to equal to zero. If we take up to be positive, we have in the positive Y direction, the force of the lift, the force on the wheels and the normal force, and in the negative y direction we have the weight of the trolley and the weight of the load, and all of this is equal to zero. Alright, so what is this F L This force that they're lifting equal to, this is gonna be equal to the weight of the trolley, plus the weight of the load, minus the force on the wheels, minus the normal force. Mhm. And so, if we have a maximum value on the force that this person can lift. Hm Well, that has to be equal to the weight of the trolley and the weight of the load. But those weights are reduced by these two forces on the right hand side, the force on the wheel and the normal force. So, these forces are going to enable the worker to lift more weight because they're reducing the right hand side of this equation. Ok. That means that we can add more weight here, because we're subtracting it here. Alright, so let's look at our answer choices. We have the force from the axle, nope, the force from the lever arm, That's not what we talked about either. The normal force from the ground and that normal force from the ground is is one of those forces that's negative on the right hand side of this equation, it's reducing the weight and that's going to enable the worker to lift more. And so c. Is true. If we keep looking the force from the wheel, that's not true. Okay, We have the force on the wheel from the ground here, but we don't have the force from the wheel. Um the worker can't lift a load greater than 160 newtons. We know that that's not true, based on what we found here and the upward force from the trolley. That's also not true. And so what we have here is answer C. Okay. The normal force from the ground is the force that we found that enables the worker to lift more weight using the trolley. Thanks everyone for watching. I hope this video helped see you in the next one