A uniform, 4.5-kg, square, solid wooden gate 1.5 m on each side hangs vertically from a frictionless pivot at the center of its upper edge. A 1.1-kg raven flying horizontally at 5.0 m/s flies into this door at its center and bounces back at 2.0 m/s in the opposite direction. (b) During the collision, why is the angular momentum conserved but not the linear momentum?

Video transcript

Hey everyone in this problem? We have a uniform door and it's kept in a vertical position by frictionless hinges along its length, and a dove is going to strike the door and bounce off with some speed in the opposite direction. And the question is asking us to state what angular momentum is conserved. A linear momentum is not based on this collision. Okay, now, when we're thinking about angular momentum, angular momentum. Okay, so l we're thinking about angular momentum, we need no net external torque. Okay, In order for angular momentum to be conserved. Now if we want linear momentum to be conserved linear momentum which is given by P then we need no net external forces. Alright, so let's think about this in the case of our problem. Well, we have the hinges. Okay, that's something that could provide some sort of external force or torque because the window is attached to the hinges that's actually going to provide an external force. Okay, So we have an external force. A net external force. That means we're not going to have linear momentum conserved. Okay, so there is a net external force. Okay, So we're not looking at answer A or C. Where there's zero external force. Okay, We know there's an external force. Then when we're looking at angular momentum while those hinges were told our frictionless. So when the window rotates with those hinges, there's not gonna be any net external torque because they're frictionless. Okay, so we have net external force. We have no net external torque. So we're gonna have d Okay, so we have angular momentum conserved. and linear momentum not conserved. Alright. I hope this video helped. Thanks for watching everyone see you in the next one.