Home » 國際課程 » A-level課程 » Details

AQA A Level Physics復習筆記4.6.5 Kinetic & Gravitational Potential Energy

Category: A-level課程, 教材筆記, 福利干貨 Date: 2022年7月7日下午5:46

Kinetic & Gravitational Potential Energy

Kinetic Energy

Kinetic energy is the energy an object has due to its?motion?(or velocity)
- The faster an object is moving, the greater its kinetic energy
When an object is falling, it is?gaining?kinetic energy since it is gaining speed
- This energy transferred from the gravitational potential energy it is losing
An object will maintain this kinetic energy unless its speed changes

5.2.4-Kinetic-energy-equation

5.2.4-Kinetic-energy-diagram

Kinetic energy (KE): The energy an object has when its moving

Worked Example

A body travelling with a speed of 12 m s-1?has kinetic energy 1650 J.If the speed of the body is increased to 45 m s-1, what is its new kinetic energy?

WE-kinetic-energy-answer-image

Gravitational Potential Energy

Gravitational potential energy (GPE) is energy stored in a mass due to its position in a gravitational field
- If a mass is?lifted?up, it will?gain?GPE (converted?from?other forms of energy)
- If a mass?falls, it will?lose?GPE (and be converted?to?other forms of energy)
The equation for gravitational potential energy for energy changes in a?uniform gravitational field?is:

5.2.2-GPE-equation

5.2.2-GPE-diagram

Gravitational potential energy (GPE): The energy an object has when lifted up

The potential energy on the Earth’s surface at ground level is taken to be equal to 0
This equation is only relevant for energy changes in a?uniform gravitational field?(such as near the Earth’s surface)

GPE v Height Graphs

The two graphs below show how GPE changes with height for a ball being thrown up in the air and when falling down

5.2.2-GPE-graphs

Graphs showing the linear relationship between GPE and height

Since the graphs are straight lines, GPE and height are said to have a?linear?relationship
These graphs would be identical for GPE against time instead of height

Worked Example

To get to his apartment a man has to climb five flights of stairs.

The height of each flight is 3.7 m and the man has a mass of 74 kg.

What is the approximate gain in the man's gravitational potential energy during the climb?

A.? ? ?13 000 J? ? ? ? ? ? ???B.? ? ?2700 J? ? ? ? ? ? ? ?C.? ? ?1500 J? ? ? ? ? ? ? ?D.? ? ?12 500 J

WE-GPE-answer-image

Exam Tip

GPE:

This equation only works for objects close to the Earth’s surface where we can consider the gravitational field to be uniform.
At A level, you might have to consider examples where the gravitational field is not uniform, such as in space, where this equation for GPE will not be relevant.

KE:

When using the kinetic energy equation, note that only the speed is squared, not the mass or the ?.
If a question asks about the ‘loss of kinetic energy’, remember?not?to include a negative sign since energy is a scalar quantity.

轉(zhuǎn)載自savemyexams

以上就是關(guān)于【AQA A Level Physics復習筆記4.6.5 Kinetic & Gravitational Potential Energy】的解答，如需了解學校/賽事/課程動態(tài)，可至翰林教育官網(wǎng)獲取更多信息。

全網(wǎng)破防！ALevel CIE數(shù)學M1疑似錯題？經(jīng)濟P2難度飆升？5月6日大考考情分析必看！