Join Our Discord

Learn Moreย ย ๐Ÿ‘‡

caret down
caret up
discord-logo

Join our Discord

1,000s of Fiveable Community students are already finding study help, meeting new friends, and sharing tons of opportunities among other students around the world! Don't miss out!ย  ๐ŸŽ‰

group of students
group of students

โš™๏ธย ap physics c: mech

ย ย >ย ย 

๐ŸŽขย Unit 3

ย ย โ€ขย ย โฑ๏ธ2 min read

3.3 Conservation of Energy โš–๏ธ

โฑ๏ธ November 5, 2020

๐Ÿ“…โŒจ๏ธ

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

ap physics c: mech study guides

Fiveable

Join Our Discord

discord-logo

Fiveable Community students are already meeting new friends, starting study groups, and sharing tons of opportunities for other high schoolers. Soon the Fiveable Community will be on a totally new platform where you can share, save, and organize your learning links and lead study groups among other students!๐ŸŽ‰

*apยฎ and advanced placementยฎ are registered trademarks of the college board, which was not involved in the production of, and does not endorse, this product.

ยฉ fiveable 2021 | all rights reserved.

2550 north lake drive
suite 2
milwaukee, wi 53211