# gcse physics question

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#1
just got this question on my gcse physics exam...is it just me, or is this impossible to figure out:

a satellite on a polar orbit has a time period of 90 mins.
the earth's gravitational field strength from that height is 10N/kg.
given that the radius of the earth is 6400 km, find the height of the satellite above the earth's surface?
0
17 years ago
#2
u use the formula, where you get use the orbital speed squared, and take away thr R value form the earths radius, u get 4 or sumthin
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#3
you mean a=(v^2)/r...but how would u work out 'v'
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#4
can i take it now that no-one can do this question...i'm dying to have a go at edexcel.
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17 years ago
#5
Originally posted by mockel
you mean a=(v^2)/r...but how would u work out 'v'
v = r(omega)

where omega = 2 pi/T

T = 90 mins = 90 * 60 = 5400 seconds.
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#6
the thing is, i don't actually know the radius of the satellite's orbit- i only know the earth's (6400 km)...so you're not able to use v=(2*pi*r)/T, or are you?
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17 years ago
#7
I just used the orbital speed formula, and then used this in the S=D/t formula... is this right??? What did u get for it??
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#8
i couldn't do it...i wrote down every formula that i knew and substituted any values that i could, hoping that i could atleast get one or two marks. i'm not sure how u would use the orbital speed formula, cos they've only given you the radius of earth.
i think this question required some major algebraic manipulation...but unfortunately i didn't have enough time to finish it.

did u do edexcel for maths as well...what did u think of that calc exam?
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17 years ago
#9
Originally posted by mockel
the thing is, i don't actually know the radius of the satellite's orbit- i only know the earth's (6400 km)...so you're not able to use v=(2*pi*r)/T, or are you?
The radius of the orbit will be (6400 x 1000 + h).

Can you not then use a = r(omega)^2, using a = 10, because the satellite is in freefall?

a = (6400 x 1000 + h)(2 pi/5400)^2.

Since when has this sort of stuff been in GCSE Physics anyway? I did my GCSEs in 2001 and we weren't required to know anything about circular motion/satellite orbits.
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#10
oh, id understand now...thanks for that.

circular motion has always been there, but is only on the extension paper (1 hr). This is just an add-on to the core syllabus, which for physics, includes particles and communications. whether you do the ext paper depends on whether your school decides to do it or not.
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17 years ago
#11
Ah ok, I wasn't aware that an extension paper existed, as we were never told about it .
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17 years ago
#12
I think you need to know the mass of the Earth. Was this given as a constant?
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