Review. While Lost-a-Lot ponders his next move in the situation described in and illustrated in Figure P12.19, the enemy attacks! An incoming projectile breaks off the stone ledge so that the end of the drawbridge can be lowered past the wall where it usually rests. In addition, a fragment of the projectile bounces up and cuts the drawbridge cable! The hinge between the castle wall and the bridge is frictionless, and the bridge swings down freely until it is vertical and smacks into the vertical castle wall below the castle entrance. (a) How long does Lost-a-Lot stay in contact with the bridge while it swings downward? (b) Find the angular acceleration of the bridge just as it starts to move. (c) Find the angular speed of the bridge when it strikes the wall below the hinge. Find the force exerted by the hinge on the bridge (d) immediately after the cable breaks and (e) immediately before it strikes the castle wall.
Lecture 1: There are 4 fundamental forces in Nature: 1. Gravitational 2. Weak 3. Strong 4. Electromagnetic Electromagnetism is the underlying force behind most observable phenomena Electricity (Lightning, electric current) Magnetism ( Electric Motors, MRI) Radiation (X-rays, Light) Chemistry Electric Charge Electric charges create electric fields Electric fields lead to forces on electric charges Moving electric charges called current create magnetic fields There are two types of charges: Positive and Negative Like charges repel and opposite charges attract Charge is conserved (cannot be created or destroyed) Charge is quantized in units of electron charge