## Final Exam help!

Hi, im in grade 11 and need some help for my final exam in physics. I have read the one of the sticky posts and im not looking for someone to do my homework, just looking for some good notes that I can use to study.

The first topic that I need help on is on "Dynamics" The question is on Fnet. "A person of mass 70kg is sitting on a 20kg slide. If two people are pulling her with two different ropes, find the persons acceleration. the force of person1 is 50N [E40*N] and the force of person2 is 60N [E25*S]
I would like this explained to me as if you were trying to teach a 10 year old this

I also need examples/notes on the following topics (I missed these class do to sickness, and I missed all the notes, tryed to get them from classmates, long story) "Sound Intesity" "Doppler Effect" and "Standing Waves". If you could explain to me these in plain english with examples, that would be of much help.

Thanks.
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 Recognitions: Gold Member Homework Help Science Advisor What exactly do you mean by [E40*N] and [E25*S]?? I assume it is a code for the direction, but I am not familiar with this notation.
 Recognitions: Gold Member Science Advisor Staff Emeritus I would assume [E40*N] is "East, 40 degrees N" (40 degrees north of east) and [E25S] is "East 25 degrees S" (25 degrees south of east) I hope that's a VERY bright 10 year old! There are a number of different ways to handle this but I would find the east and nort components of each force. The first has n component 50*cos(40) and e component 50*sin(40). The second has n component -60 cos(25) and e component 60 sin(25). Add those to get the n and e components of the force on the person and sled. the "Pythagorean" theorem to get the actual magnitude of that force. Finally use "force equals mass times acceleration" to find acceleration.