Textbook Reading: Read the definition and formula for Newton’s 2nd Law on p.115. If you don’t understand it at first, read the paragraphs around the definition (which is between 2 red lines) to help.
Note, the book uses ΣF, where I use Fnet. They mean the same thing.
Pre-reading question: Conceptual question 5 on p. 139
Newton’s 2nd Law Concepts
Textbook reading: Section 5-3, pages 114-122 lays out EXACTLY how to do Newton’s 2nd Law problems. If you’re in a rush, there’s a summary on page 118. The summary begins “We can summarize” and ends “to indicate a free-body sketch.” The example 5-1 on pages 119-120 follows these steps, so you can see them in action. If you have the time, that entire section is really great on understanding how to solve these problems. Note, the book uses ΣF, where I use Fnet. They mean the same thing.
Post-reading question: Referring to the pre-reading question: If the girl has a mass of 50kg and an downward acceleration of 3m/s/s, what is the tension in the string? (Hint: tension here is like the normal force with the elf from the video.)