Splung.com Physics Forum Forum Index Splung.com Physics Forum
Discuss physics or ask questions. Part of the Splung.com physics web site.
 
   SearchSearch   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

velocity and gravitation

 
Post new topic   Reply to topic    Splung.com Physics Forum Forum Index -> Physics Help. Ask a Physics Expert
View previous topic :: View next topic  
Author Message
canicon25



Joined: 03 Jan 2012
Posts: 2
Location: canada

PostPosted: Tue Jan 03, 2012 10:44 pm    Post subject: velocity and gravitation Reply with quote



Please help me. I cannot solve this.

I tried this approach

delta Ek+Q = delta -1/2 Ep
(0.5)mv^2 = -GMm/r1 - -GMm/r2 - Q

Does this look like the correct formula?
Back to top
View user's profile Send private message
hepcj
Site Admin


Joined: 23 Jun 2007
Posts: 125

PostPosted: Sat Jan 07, 2012 11:26 pm    Post subject: Reply with quote

The block falling to Earth has an initial potential energy due to its height above the Earth and as it falls, this is changed into kinetic energy and heat energy. You have the right idea but the 1/2 Ep is wrong.

change in potential energy = change in kinetic energy + heat produced

PE = -(GMm/r)
KE =1/2 mv^2
Q = heat energy


The final result will not depend on the mass m.
-GM[(1/rf)+(1/ri)] -Q= 1/2 v^2 , rf is the final height, ri is the initial height.
Back to top
View user's profile Send private message Send e-mail
canicon25



Joined: 03 Jan 2012
Posts: 2
Location: canada

PostPosted: Sun Jan 08, 2012 1:52 am    Post subject: Reply with quote

yes. i made the critical error of using this

delta KE = -0.5 delta PE

which only applies to circular orbits

i needed to use and subsequently obtain the correct answer using

delta KE +Q = -delta PE

thank you for your replies.
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    Splung.com Physics Forum Forum Index -> Physics Help. Ask a Physics Expert All times are GMT
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


© Copyright 2010 Splung.com