Go Back   Physics Help Forum > High School and Pre-University Physics Help > Energy and Work

Energy and Work Energy and Work Physics Help Forum

Reply
 
LinkBack Thread Tools Display Modes
Old Mar 26th 2009, 01:58 AM   #1
ohm
Senior Member
 
Join Date: Mar 2009
Location: Yadupatti Bazar,Sitamarhi
Posts: 131
source of energy

Let us consider a body is at a height of 2m from the earth.According to definition it has potential energy of magnitude mgh and kinetic energy is zero.Now what is the source of its energy ? is it due to gravitational force of eath or is any reason. What will be its potential energy if i bring it in universe?
Now if body starts falling towards the earth,then P.E. will convert into K.E.
On the earth velocity is zero.Hence P.E. and K.E. both will be zero.Is body now energyless.If it is mass, then it was at the all time.
Further, on the earth ,body is at rest, but earth is moving?what about this?
ohm is offline   Reply With Quote
Old Mar 26th 2009, 03:12 AM   #2
ohm
Senior Member
 
Join Date: Mar 2009
Location: Yadupatti Bazar,Sitamarhi
Posts: 131
Thumbs down

I didn't get any help till now? Please help anyone. Thanks for that
ohm is offline   Reply With Quote
Old Mar 26th 2009, 05:08 AM   #3
Physics Team
 
Join Date: Feb 2009
Posts: 1,425
Yes the source of energy is due to the grav attraction of the earth. Work has to be done against this to raise it to the height h. It already is in the universe! All things known to us are already in the universe. If you mean Outer space even then the major contribution will be from the earths field. else you will have to calculate its P.E. with respect to all the other objects inthe universe and then total it.
When it hits the earth the K.E. gets converted into sound energy, heat energy etc. so the total energy remains constant. So the energy of the body now wil be equal to its rest mass only.
The earth always was moving .If you wish to consider its energy then include it in the problem right at the beginning and the total energy will be found constant.
Whwnever you consider any problem fix a frame of reference first.
physicsquest is offline   Reply With Quote
Old Mar 26th 2009, 10:45 PM   #4
ohm
Senior Member
 
Join Date: Mar 2009
Location: Yadupatti Bazar,Sitamarhi
Posts: 131
thanks for reply. But in outer space if I want to calculate P.E. (say w.r.t MOON),then which formula we should use?
ohm is offline   Reply With Quote
Old Mar 27th 2009, 02:29 AM   #5
Physics Team
 
Join Date: Feb 2009
Posts: 1,425
Well if there is a mass m very close to the moon, ( at a small height compared to its radius), then you can use P.E = mgh where g here is the acceleration due to gravity on the surface of the moon (which is roughly 1/5th that on earth i think)

A more general formula is Grav P.E. = -G M m / R where M = mass of the moon, G = universal gravitation constant and R is the distance from the centre of the moon.
physicsquest is offline   Reply With Quote
Old Mar 27th 2009, 11:05 PM   #6
ohm
Senior Member
 
Join Date: Mar 2009
Location: Yadupatti Bazar,Sitamarhi
Posts: 131
thaks! You have given a -ve sign in ur formula. what indicates it?
consider that there are only two heavenly bodies EARTH and MOON.
can we say that the total P.E. in the body=P.E. w.r.t. EARTH + P.E. w.r.t. MOON ?
if it is,then practically we can say that a body in outer space has unlimited P.E. right or wrong?
pls help me.
ohm is offline   Reply With Quote
Old Mar 28th 2009, 12:33 AM   #7
Physics Team
 
Join Date: Feb 2009
Posts: 1,425
If there are only two heavenly bodies, what you say is right.
However P.E. is not unlimited in outer space. As you go further away R increases so the magnitude of this energy decreases.
physicsquest is offline   Reply With Quote
Reply

  Physics Help Forum > High School and Pre-University Physics Help > Energy and Work

Tags
energy, source



Thread Tools
Display Modes


Similar Physics Forum Discussions
Thread Thread Starter Forum Replies Last Post
Thesis Source help please.... darkkensai7 General Physics 4 Nov 14th 2013 04:34 AM
Analytical balance source needed... Squint General Physics 0 Apr 15th 2013 07:12 AM
Evaluating Source Matrix in an open system joysoumitra Quantum Physics 0 Dec 3rd 2011 10:14 AM
Motion of point mass under two central forces -- source of one stationary one moving. taureau20 Kinematics and Dynamics 0 Sep 27th 2008 02:52 AM


Facebook Twitter Google+ RSS Feed