A light rope is attached to a block with mass 4.00 kg that rests on a frictionless, horizontal surface. The horizontal rope passes over a frictionless, massless pulley, and a block with mass m is suspended from the other end. When the blocks are released, the tension in the rope is 15.0 N. (a) Draw two free-body diagrams: one for each block.

Video transcript

Hey everyone today, we're dealing with a pulley system and we're being told that a 2.9 kg box rests on a horizontal of frictionless surface. A string is attached to the box that runs through a massless and frictionless pulley that suspends another box of mass M with its other end The box are released and the tension in the string is found to be 9.8 newtons. And with this information, we're being asked to draw a free body diagram for each box. Now, we don't really need our values here. We can just go ahead and start drawing the forces acting upon each box independently. So, let's start with Box A let us say that this is Box A and is resting on a horizontal surface. Mhm is resting on a horizontal surface. So, as with anything that has mass, especially on Earth, right? We will have a force due to gravity pointing towards the center of the earth. That will be the weight. Right? So we have a weight force that points directly down. This should just mass into the force of acceleration due to gravity. Now, we also have a normal force because the block is resting on a surface and the electrostatic repulsion between the surfaces will prevent it from will prevent the box from falling into said surface. And the normal force will be perpendicular to the horizontal surface itself. And we can see that it forms a right angle and it will also have a magnitude of mass and energy. Now the string is pulling because it's on a pulley, right? And we can't have tension. The tension is pointing towards the box. So the force due to tension oops the force due to tension. Well point in this direction to the right. Now looking at box B, it starts off pretty similar. We have a force due to the gravity so we have weight equal to MG. However we don't have a normal force, right? Because it's not in contact with any surface, we don't have any electrostatic repulsion between surfaces to give us a normal force. All we do have is the tension in the rope which will again be pointing away from the box itself. So have tension here. So that will be the force diagram or free body diagram for each box independently. For Box A. And box B. I hope this helps. And I look forward to seeing you all in the next one.