Gravitational Potential Energy of a satellite

[Victorian91]

Can someone help me..

A satellite of mass 100kg revolves round the Earth in a circular orbit of radius 2R where R is the radius of the Earth. Determine the energy needed to move the satellite to a new orbit of radius 3R.

Thanks a lot.

 

[phyzmatix]

Can someone help me..

A satellite of mass 100kg revolves round the Earth in a circular orbit of radius 2R where R is the radius of the Earth. Determine the energy needed to move the satellite to a new orbit of radius 3R.

Thanks a lot.

Hi Victorian91! Welcome to PF

You have to show what you've done/tried first before we can help.

 

[Victorian91]

Okay..
This is how i did my solution to this problem..

In the old orbit, Ui = - GMm/2(2R)

In the new orbit, Uf = - GMm/2(3R)

Energy needed U = Uf -Ui

= GMm/ 12R

= 5.2X10^8 J

Is this correct?

Or it should be just putting in 2R and 3R..

Thanks..

 

[adriank]

In the old orbit, Ui = - GMm/2(2R)

In the new orbit, Uf = - GMm/2(3R)

Why do you have the 2 in the denominator of each? I think you should have Ui = -GMm/2R and Uf = -GMm/3R. I'm curious why you thought the extra 2 came in.

 

[Victorian91]

Yes I agree with you..

Just that I was skeptical when my textbook included the 2(2R) and 2(3R)

That is why I post this ..

Could anyone know why?

 

[adriank]

I have no idea why the textbook included the extra 2. Are you sure that's exactly the problem in the book?

Also, out of curiosity, which textbook is it?

 

[Victorian91]

Well,

Its PRE - U Text STPM
Physics (Volume 1 )

Maybe a printing error..

 

[skiing4free]

Okay..
This is how i did my solution to this problem..

In the old orbit, Ui = - GMm/2(2R)

In the new orbit, Uf = - GMm/2(3R)

Energy needed U = Uf -Ui

That is correct but without the 2* that just seems weird, when i calculated the energy required i got an answer of 1.04x10^9J... What is the correct answer?