BF2S Forums Help with my Energy exam plzkthx

james@alienware wrote:

Gravitational potential energy = mass x gravity x height   


gravity = 9.81

yeah, I know that, but I want an example.

just put some numbers in for me. I don't know what kind of measurements you need. (cm? m? g? kg?)

james@alienware wrote:

Height always in metres, so say 2m.
Mass always in kilograms, so say 5kg.
Gravity is 9.81, approximately 10.


GPE = 5 x 10 x 2


GPE = 100 Joules

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Hope that helps!

Jenspm wrote:

Ok, so I can explain it like this?


The formula for Pottential Energy is Ep = mgh.

This means that the mass x gravity x height = Potential Energy.

If we, for example, held a 1kg rock 2 meters above the ground, by the sea level where the gravity is 9.81 m/s^2, we could quickly find the Pottential energy:

1 x 2 x 10 = 20 Joule.

The rock contains a pottential energy of 20 Joule, which....



I need a kind of ending. Like, what is this energy used for? Does it transform to heat and sound when it hits the ground?

that is correct. the joules is the potential energy stored inside it, which increases as it gets higher. I am not sure how to actually explain it.....

Wikipedia wrote:

Potential energy is also known as the work done by a certain force (such as gravitational force or Coulomb force) when the relative positions of objects are changed within a physical system. The phrase 'potential energy' was coined by William Rankine.[1] In other words, it is the work done when an object is moved from one point to another. Conceptually, potential energy can be thought of as the energy stored in an object as a result of the work done to bring it to that position from a reference point. When an object moves from one point to another, and there is a potential difference as a result of this, then work is performed. Potential energy is so named because this stored energy or work has the potential to change the state of other objects when released.

Wikipedia ftw, it is kinda confusing though.

TimmmmaaaaH wrote:

Jenspm wrote:

Ok, so I can explain it like this?


The formula for Pottential Energy is Ep = mgh.

This means that the mass x gravity x height = Potential Energy.

If we, for example, held a 1kg rock 2 meters above the ground, by the sea level where the gravity is 9.81 m/s^2, we could quickly find the Pottential energy:

1 x 2 x 10 = 20 Joule.

The rock contains a pottential energy of 20 Joule, which....



I need a kind of ending. Like, what is this energy used for? Does it transform to heat and sound when it hits the ground?

that is correct. the joules is the potential energy stored inside it, which increases as it gets higher. I am not sure how to actually explain it.....

Wikipedia wrote:

Potential energy is also known as the work done by a certain force (such as gravitational force or Coulomb force) when the relative positions of objects are changed within a physical system. The phrase 'potential energy' was coined by William Rankine.[1] In other words, it is the work done when an object is moved from one point to another. Conceptually, potential energy can be thought of as the energy stored in an object as a result of the work done to bring it to that position from a reference point. When an object moves from one point to another, and there is a potential difference as a result of this, then work is performed. Potential energy is so named because this stored energy or work has the potential to change the state of other objects when released.

Wikipedia ftw, it is kinda confusing though.

So this means that I have used 20 Joules of my energy to move this rock 2 meters in the air? And the these 20 Joules are transfered into the rock as Potential Energy? And then I let the wrock fall to the ground, and it gets a Kinetic energy of 20 Joules, before it hits the ground and the 20 Joules of energy transform into Heat, Sound and more?

Last edited by Jenspm (2007-06-04 04:00:12)

namsdrawkcaB wrote:

are you fucking retarded? you cant even put some numbers in?? jesus christ lazy ftw

GTFO.

Jenspm wrote:

TimmmmaaaaH wrote:

Jenspm wrote:

Ok, so I can explain it like this?


The formula for Pottential Energy is Ep = mgh.

This means that the mass x gravity x height = Potential Energy.

If we, for example, held a 1kg rock 2 meters above the ground, by the sea level where the gravity is 9.81 m/s^2, we could quickly find the Pottential energy:

1 x 2 x 10 = 20 Joule.

The rock contains a pottential energy of 20 Joule, which....



I need a kind of ending. Like, what is this energy used for? Does it transform to heat and sound when it hits the ground?

that is correct. the joules is the potential energy stored inside it, which increases as it gets higher. I am not sure how to actually explain it.....

Wikipedia wrote:

Potential energy is also known as the work done by a certain force (such as gravitational force or Coulomb force) when the relative positions of objects are changed within a physical system. The phrase 'potential energy' was coined by William Rankine.[1] In other words, it is the work done when an object is moved from one point to another. Conceptually, potential energy can be thought of as the energy stored in an object as a result of the work done to bring it to that position from a reference point. When an object moves from one point to another, and there is a potential difference as a result of this, then work is performed. Potential energy is so named because this stored energy or work has the potential to change the state of other objects when released.

Wikipedia ftw, it is kinda confusing though.

So this means that I have used 20 Joules of my energy to move this rock 2 meters in the air? And the these 20 Joules are transfered into the rock as Potential Energy? And then I let the wrock fall to the ground, and it gets a Kinetic energy of 20 Joules, before it hits the ground and the 20 Joules of energy transform into Heat, Sound and more?

No gravitational potential energy is how much energy is 'stored' in the rock...as in how much it has being held in this position 2metres up.

But I guess you could see it as how much energy it takes to get it there, but that's not technically correct.

Jenspm wrote:

Ok, so I can explain it like this?


The formula for Pottential Energy is Ep = mgh.

This means that the mass x gravity x height = Potential Energy.

If we, for example, held a 1kg rock 2 meters above the ground, by the sea level where the gravity is 9.81 m/s^2, we could quickly find the Pottential energy:

1 x 2 x 10 = 20 Joule.

The rock contains a pottential energy of 20 Joule, which....



I need a kind of ending. Like, what is this energy used for? Does it transform to heat and sound when it hits the ground?

sounds fine to me but am i wrong in saying that they prefer it if you put the force of gravity as 9.81 m/s/s

i am probably wrong

Sarrk wrote:

Get yourself a graphic calculator, TI-83/84, and write all the formulas down into it.

Or be friends with the programming genius in your school and get programs that automatically solve what you need and even provide the steps for how you supposedly did it

Jenspm wrote:

Actually, it is...

Work = Force x Stretch

(1 kg = 10 Newton) x 2 meters = 20 Nm = 20 Joules


no?

Nah...that's not quite right:

Work = force x distance



That was if YOU were moving the rock to the height.

As I said, gravitational potential energy doesn't involve the rock moving, it's just there.

Jenspm wrote:

So, my Oral exam in Energy is on Wednesday, and we are pulling some physyics into the thing.

What I need help with is an Example of how to find the Pottential Energy in a rock that is held in the air.

http://upload.wikimedia.org/math/7/7/8/ … a5bc6b.png

Prefferably some easy numbers so I can act like I'm doing it in my head.

Yes, I know, Norway is faaar behind you guys in this stuff.

thx

Epot = mass * height * gravitational pull

mass = the weight of the object you are working with.. eg. the stone.. The weight is measured in [kg], kilo grams (1000's grams).

height = is the height from which the stone is dropped. The height is measured in [m], meters since you are from norway..

gravitational pull = Is a constant (something thats always there..) I see you are from Norway so its aproximately the same as here in Denmark.. which will be 9.82 [m/s^2] (meters per second squared)
Its the "rate" that the earth pulls everything towards it with..

Epot = is the potential energy the stone has stored in it. eg. if the stone is at the surface of the earth the height is "0". and the two other variables times 0 = 0.. that makes sence. because a stone sitting on the ground wont hurt you if it hit you.. if for instance a 1kg stone is dropped from a height of 10m's:

Epot = 1kg * 10m * 9,82m/s^2 = 98,2 J

Energy is measured in [J], Joules..

If you want potential energy explained in a "easy to understand way":
its the amount of "damage" the stone could do.., or its the amount of "work" the stone could do...

Energy

here is some misc information you can use to explain the term energy.. (some of it has been mentioned before)

Energy comes from "force" (no, not from StarWars..)

Newton's 2nd law: F = m*a

F = Force, measured in [N], Newton
m = is the mass like before
a = acceleration, measured in [m/s^2]

Energy is basically a Force applied over a distance.. eg. if a man pulls a cart.

gravity comes from Newtons 2nd law:
F = m*g

"g" is the same as "a".. "g" is just used when talking about the earths acceleration of items..

so the only difference between F = m*g and Epot = m*g*h is the height, which is a distance..
and thats how force becomes energy (in this case)

It dosnt sound like its physics at a high level so I'll leave the units out of this.. although if you want me to post some theory about that or get more scientific, just say so (or if you want it in danish/(norwegian) I could do that too...

sorry if some things are misspelled or hard to read..

good luck with it..

Z-trooper, fyi, Mass does not equal weight. Mass is the amount of material in an object, weight is dependent on gravity. Something has a mass of x kg, while is has a weight of y N.

Converting this to english units: Mass = x slugs (this is a very confusing unit, as there are two different types of slugs, oddly enough; if you would like a better explanation, let me know), weight = y pounds.

My physics class sucks.  Everyone is busy stealing shit and someone blew up the microwave.