A factory worker pushes a 30.0-kg crate a distance of 4.5 m along a level floor at constant velocity by pushing horizontally on it. The coefficient of kinetic friction between the crate and the floor is 0.25. (c) How much work is done on the crate by friction?

Video transcript

Hey everyone today, we're being asked to find the work done by friction on a desk that is being pushed by a person. So let's figure out or look at the question and determine some important figures. We know that the desk is 15 kg. It's moving at a constant speed And it is on a 10 m horizontal concrete surface. The coefficient of kinetic friction between the two surfaces that when the concrete is 0.3. So let us go ahead and write down a few important formulas and things we should recall. So we know that the force of kinetic friction que is equal to the coefficient of kinetic friction multiplied by the normal force denoted by m the surface is horizontal, right? We have a horizontal surface and we have a desk. Let us say this desk, which means the normal force. If there is a force going down by gravity will be directly opposite, see or directly perpendicular. I should say, to the horizontal surface in this case, because it is horizontal, that means that the normal force, that means normal force will be equal to MG due to the weight. Let me write this as a lower case for weight is also equal to MG. Remember we are moving at a constant speed and kinetic friction is parallel. So kinetic friction is parallel, It runs parallel to the surface to surface and opposite to the motion. So if the motion is going this way, let's say it's being pushed to the left, then the force of kinetic friction, let me write that in blue. If this is the force applied, say force app then the force of kinetic friction will go opposite to that. Therefore the work done. Therefore work done by the force of friction will be negative because it is acting opposite to the direction of the force being applied. So with all this in mind we can go ahead and write out how we're going to find the work done by friction. So they work due to friction is equal to the force of kinetic friction, multiplied by the distance traveled. That is the definition of work is forced by distance or forced into distance. I should say we know that the uh force of kinetic friction should be negative and we know that our normal force is equal to MG. So we can substitute in these values and now expanding. We get 0.3. Oops, Let me uh let me rewrite this. Got to include our negative is negative. 0.3 Multiplied by a mass of kg. G. Is the acceleration due to gravity or 9.8 m per second squared. And the distance traveled is 10 m in the horizontal direction. Simplifying all of this, we get a final answer of negative 441 jewels. This means the work done by friction on the desk will indeed be answer choice B -441 Jules. I hope this helps. And I look forward to seeing you all in the next one