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Satellite orbit - A2 Physics watch

1. I keep getting the wrong answer on this question and can't see why

A satellite is required to orbit the Earth once every 12 hours. Calculate the necessary radius of its orbit.
if you use T^2 = [(4xπxπ )/(GM)] x r^3
you get (43200)^2 = [(4xπxπ )/(4x10^14)] x r^3 //M = 6.0x10^24(kg)
then r^3 = 1.89x10^22
so r = 26.6x10^6(m)

However the answer should be 90.9x10^6(m) but I can't see where I am going wrong.
2. Seems right to me, but i could be making the same mistake that you are. Is the question from a textbook? Its not unusual for a textbook to publish the answers wrong.
3. (Original post by Chris2505)
I keep getting the wrong answer on this question and can't see why

if you use T^2 = [(4xπxπ )/(GM)] x r^3
you get (43200)^2 = [(4xπxπ )/(4x10^14)] x r^3 //M = 6.0x10^24(kg)
then r^3 = 1.89x10^22
so r = 26.6x10^6(m)

However the answer should be 90.9x10^6(m) but I can't see where I am going wrong.
Got the same answer as you, dont think the book will be wrong though as its quite big difference
4. (Original post by Im_a_cyborg)
Seems right to me, but i could be making the same mistake that you are. Is the question from a textbook? Its not unusual for a textbook to publish the answers wrong.
Yeah from a textbook but htere has been the odd mistake in it but usually just a typo, not a calculation error.
5. Maybe they only had pi once in there? It looks like it's out by a factor of ~3...
6. (Original post by Chris2505)
Yeah from a textbook but htere has been the odd mistake in it but usually just a typo, not a calculation error.
I have come across a few errors in the answers in mine. Especially that OCR Physics 2 one.
7. well i also got the same answer maybe the mark scheme is wrong
8. Thanks anyway, must be a book error, again...

90.9Mm does seem a very big distance though!!
9. (Original post by Chris2505)
I keep getting the wrong answer on this question and can't see why

if you use T^2 = [(4x?x? )/(GM)] x r^3
you get (43200)^2 = [(4x?x? )/(4x10^14)] x r^3 //M = 6.0x10^24(kg)
then r^3 = 1.89x10^22
so r = 26.6x10^6(m)

However the answer should be 90.9x10^6(m) but I can't see where I am going wrong.
they didnt use 4pi^2 to get their answer beats me why they didnt include it

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