๐Ÿ“š

All Subjects

ย >ย 

โš™๏ธย 

AP Physics C: Mech

ย >ย 

๐ŸŽข

Unit 3

3.3 Conservation of Energy โš–๏ธ

2 min readโ€ขnovember 5, 2020


AP Physics C: Mechanicsย โš™๏ธ

Bookmarkedย 1kย โ€ขย 54ย resources
See Units

3.3: Conservation of Energy โš–๏ธ

The Law of Conservation of Energy is as follows:
If only forces internal to the system are acting on an object in a physical system, then the total change in mechanical energy is zero.
This essentially means that energy in a system can change its form without energy leaving the system.
The equation version of this law is:
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-cnnS9hCgm7Ld.PNG?alt=media&token=878b0c5b-6344-47b9-b592-96edf7d530ae
Which states that the total mechanical energy, ME, is the sum of the potential, U, and kinetic energy, K, in a system.
When a nonconservative force acts on a system, work is done, and this work does change the total mechanical energy of the system! This work can be found in a simple equation:
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-yJnGM8tC7EAR.PNG?alt=media&token=943557cc-c684-46c0-8409-65d75c34ba52
When you have a conservative system (total energy is a constant), you can use the Law of Conservation of Energy to calculate unknown quantities in many scenarios like rollercoasters, ramps, pendulums, and springs.
You can use this PhET simulation to see conservation of energy in practice!

Practice Questions

1.
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F3-4tw7x6QBEvZn.png?alt=media&token=061eada3-ec03-4734-b771-329e17d0017b

Taken from CollegeBoard

Answer:

Always, always, always remember to state that you're using conservation of energy! You should begin all energy problems by stating whether or not energy is conserved as that typically earns you a point.
Then identify what is occurring at the beginning of the problem and what is occurring at the end in order to determine how energy is transferred.
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2Fanswer%203-39cqCYqb87rV.png?alt=media&token=7e22eaa8-2f3b-4ad3-84c1-a6933220d29d
2.
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2Fq%203-BXfm0fFGeu98.png?alt=media&token=b05ff8da-8458-4640-ba61-20b25b11c868

Answer:

AP loves to make students think about proportions, so whenever asked about comparing the same variable, try to find an equation you can use! Don't try to plug in anything to the equation, just look at what coefficients are different at the two moments in time you are examining.
Additionally, you should notice that they wanted you to look at the relationship you discovered in a previous part of the question.
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2Fan%203-dN192HGLtZ1j.png?alt=media&token=1d5d7627-850b-49cf-b5c9-7debaa9b6803
3.
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-y6cp1tTe7yXk.png?alt=media&token=c365137e-e58f-4606-8af9-a9407c08f6ab

Answer:

Same process as the previous part!
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-T1Iy3ijdul8a.png?alt=media&token=29a88ec7-1ac4-4a07-91b5-a0562df9a4ec
4.
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-QkDV7joWehTI.png?alt=media&token=2548aae4-d211-4155-9829-2cbbcf2942a5

Answer:

If you haven't learned about differential equations in calculus that's okay! But once you do, you should notice that AP will never ask you to solve them due to the time crunch you are in unless they are incredibly simple. Additionally, take note that you did not have to use all the variables they listed in the question. Most FRQs will focus on more than one unit of physics and you will have to be aware of the intersections between things like forces and energy.
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-uYHrmcculcfg.png?alt=media&token=2a880780-11ef-40b1-9324-18411c22cf76
5.
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-eWlYgCjOPRoH.png?alt=media&token=0fa3906c-11a6-4662-aeb6-07d7c6b0efa8

Answer:

Separating variables is always the first step in resolving a differential equation, then integration. Notice that if it is a definite integral they want you to place the bounds/ use the correct limits and if it is an indefinite integral(which is not common in the realm of physics) they will give you a freebie point for just stating +C!
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-3uJgNWoUCths.png?alt=media&token=08f01f54-4474-4088-95e3-6063d41eb302

Was this guide helpful?

Join us on Discord
Thousands of students are studying with us for the AP Physics C: Mechanics exam.
join now
Hours Logo
Studying with Hours = the ultimate focus mode
Start a free study session
๐Ÿ” Are you ready for college apps?
Take this quiz and find out!
Start Quiz
Browse Study Guides By Unit
๐Ÿ™Exam Reviews
๐Ÿš—Unit 1: Kinematics
๐Ÿš€Unit 2: Newton's Laws of Motion
๐ŸŽขUnit 3: Work, Energy, and Power
๐ŸŽณUnit 4: Systems of Particles and Linear Momentum
๐ŸšฒUnit 5: Rotation
๐ŸŒŠUnit 6: Oscillations
๐ŸชUnit 7: Gravitation
FREE AP physics c m Survival Pack + Cram Chart PDF
Sign up now for instant access to 2 amazing downloads to help you get a 5
Join us on Discord
Thousands of students are studying with us for the AP Physics C: Mechanics exam.
join now
๐Ÿ’ช๐Ÿฝ Are you ready for the Mechanics exam?
Take this quiz for a progress check on what youโ€™ve learned this year and get a personalized study plan to grab that 5!
START QUIZ
Play this on HyperTyper
Practice your typing skills while reading Conservation of Energy โš–๏ธ
Start Game
๐Ÿ“ฑ Stressed or struggling and need to talk to someone?
Talk to a trained counselor for free. It's 100% anonymous.
Text FIVEABLE to 741741 to get started.
ยฉ 2021 Fiveable, Inc.