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Calculate the gravitational field strength g at the radius of 15 300 km?

What equation do I use this? I am so confused because it seems like I have no other info. Thanks in advance

Here is the paper and markscheme, question 22bii http://www.ocr.org.uk/Images/171727-unit-h556-01-modelling-physics-sample-assessment-materials.pdf
Reply 1
Avatar for AnonEcon
AnonEcon
3
Use g=GM/r^2. Plug in r=15300km and M=mass of Earth= 6*10^24 (id learn this)
Original post by BrainJuice
What equation do I use this? I am so confused because it seems like I have no other info. Thanks in advance

Here is the paper and markscheme, question 22bii http://www.ocr.org.uk/Images/171727-unit-h556-01-modelling-physics-sample-assessment-materials.pdf


g=GM/r^2. It says in the question that the satellite orbits the Earth. So, G = 6.67x10^-11, M= mass of Earth and r=15,300*1000. Plug it all in and it should come out as 1.71 N/kg to 3sf.
Reply 3
Avatar for BrainJuice
BrainJuice
OP
15
Original post by nav1234567
g=GM/r^2. It says in the question that the satellite orbits the Earth. So, G = 6.67x10^-11, M= mass of Earth and r=15,300*1000. Plug it all in and it should come out as 1.71 N/kg to 3sf.


Oh. Thanks haha,

Do you know why teh mark scheme says:

g = (6400/15300)2 x 9.81 g = 1.72 (N kg–1
[QUOTE="BrainJuice;72059738"]Oh. Thanks haha,

Do you know why teh mark scheme says:

g = (6400/15300)2 x 9.81 g = 1.72 (N kg–1[/QUOTE

Basically both answers are correct they have just simplified it and not bothered to use an equation. They have set up a ratio.
Reply 5
Avatar for BrainJuice
BrainJuice
OP
15
[QUOTE="nav1234567;72059796"]
Original post by BrainJuice
Oh. Thanks haha,

Do you know why teh mark scheme says:

g = (6400/15300)2 x 9.81 g = 1.72 (N kg–1[/QUOTE

Basically both answers are correct they have just simplified it and not bothered to use an equation. They have set up a ratio.


Yeah because the mass of the earth isn't on the formula sheet I think. I'm still quite confused with their expleation but thanks nevertheless.
[QUOTE="BrainJuice;72059916"]
Original post by nav1234567


Yeah because the mass of the earth isn't on the formula sheet I think. I'm still quite confused with their expleation but thanks nevertheless.


You have to know that g is directly prop to 1/r^2. Turn this into an equation and you get g=k/r^2. Solve for K and you get g*r^2=K. g1*r1^2=g2*r2^2. Therefore 9.81*6400^2= g2*15,300^2. therefore g2= 6400^2/15,300^2 * 9.81.
Reply 7
Avatar for BrainJuice
BrainJuice
OP
15
[QUOTE="nav1234567;72060032"]
Original post by BrainJuice


You have to know that g is directly prop to 1/r^2. Turn this into an equation and you get g=k/r^2. Solve for K and you get g*r^2=K. g1*r1^2=g2*r2^2. Therefore 9.81*6400^2= g2*15,300^2. therefore g2= 6400^2/15,300^2 * 9.81.



Thank you very much

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