https://youtu.be/YrMb_PDwJSw
PHYS 1101: Lecture Five, Part One
Welcome to Lecture 5. Lecture 5 finishes off Chapter 2 for us, and this is where we really are going to start doing some physics. We now have the tools that we need to solve some real problems.
I’m going to start off the lecture, as usual, with a warmup quiz question for you. And for this question, it’s a little trickier. Again, consider using the discussion board to sort it out. This time I’m going to raise the stakes a little for you. I’ll give everybody +5 if 70% of the class gets it right. Otherwise, +1.
And here’s my question to you. I want you to watch this little video. Focus on the motion. Sketch a motion diagram. Imagine what the motion diagram is, and then the question asks you what the acceleration is going to be at the highest point.
What you’re watching here is a ball being shot straight up. Probably it will look a little choppy to you, but imagine doing this in real life. You know that the motion would be smooth. The ball slows down, turns around, and then speeds up on the way back down.
So, draw your motion diagram, sketch in your velocity vectors between each point, and then really think about what the acceleration vectors would be between all the adjacent velocity vectors. What you need to answer this question is just a feeling for what’s the sign of that acceleration vector. And I want you to answer that question about the instant at the highest point.