The radius of the Moon's orbit will be halved, and its tangential velocity will double. The trick here is to keep the Moon's angular momentum constant when you suddenly double Earth's mass. You need two equations: Gravitational force = centripetal force, and (initial angular momentum) = (final angular momentum). Solve them simultaneously for the final velocity and orbital radius. Do everything in algebra, and you'll get all your answers without a calculator. An excellent problem! Thank you!
Vickie
-----Original Message-----
From: Forum for Physics Educators [mailto:PHYS-L@list1.ucc.nau.edu]On
Behalf Of David Abineri
Sent: Wednesday, October 13, 2004 3:48 PM
To: PHYS-L@LISTS.NAU.EDU
Subject: Satelite Motion
Can someone give me a way to think about this question?
If the earth's gravity doubled, how would the moon's orbit be affected?
I am getting tangled up in having too many variables and it is not at
all obvious what might happen. Would the results be different if it
happens instantaneously rather than incrementally?
Is there a way to look at this that might make it clear for students?