04_2d - Lesson 4: 2-D Collisions We now need to turn our...

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Lesson 4: 2-D Collisions We now need to turn our attention towards questions involving objects that collide in two dimensions (2D). In the previous section we were looking at only linear collisions (1D), which were quite a bit simpler (mathematically) to handle . Now we need to figure out some ways to handle calculations in more than 1D. You actually learned about this in Physics 20 in the vectors section. First, let’s look at drawing some diagrams of some common collisions, then we’ll worry about the calculations… Example 1 : Sketch a diagram that represents the collision between two moving pool balls (of equal mass) that strike each other with an angle of 30 ° between them. They do not stick together. We need to show what happens before and after the collision. So far this is just a rough sketch, since we weren’t told anything about their velocities or the angle that they traveled away at. All that we’re doing at this point is showing that we know that the balls should move off in directions similar to the ones shown here. Example 2 : Sketch a diagram that represents the collision between a moving pool ball that strikes a stationary pool ball. They move off with an angle of 60 ° between them. 10/28/2009 © studyphysics.ca Page 1 of 6 / Section 9.4 Illustration 1: Collision between two moving balls After Before 30 o Illustration 2: Collision between one moving and one stationary ball After Before 60 o
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In examples like this you will often see that the question refers to the collision as “ glancing .” This simply means that the objects do not hit head on. If they did hit head on then the collision would be 1D, not 2D. Now we need to start looking at some questions with calculations. Some people are more comfortable doing these questions using components, others like using cosine and sine laws. Since not everyone knows cosine and sine laws, we'll only use components in the following examples. Example 3 : A 1.20 kg red ball moving to the right at 17.1m/s strikes a stationary 2.31 kg blue ball. If the final velocity of the red ball is 13.5m/s at 23.0 ° above the horizontal, determine the final velocity of the blue ball. A sketch is always a good idea, even if you're not asked for one.
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04_2d - Lesson 4: 2-D Collisions We now need to turn our...

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