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canicon25

Joined: 03 Jan 2012
Posts: 2

 Posted: Tue Jan 03, 2012 10:44 pm    Post subject: velocity and gravitation 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?
hepcj

Joined: 23 Jun 2007
Posts: 125

 Posted: Sat Jan 07, 2012 11:26 pm    Post subject: 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.
canicon25

Joined: 03 Jan 2012
Posts: 2

 Posted: Sun Jan 08, 2012 1:52 am    Post subject: 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.
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