Gravitational Fields

  • Thread starter F.B
  • Start date
  • #1
F.B
83
0
I am stuck on these problems i really dont know how to do them.So can any one please help me. Can you explain how to do these questions.

A 620 kg satellite above the earth's surface experiences a gravitational field strength of 4.5 N/kg.

a) Knowing the gravitational field strength at earth's surface abd earths radius, how far above the Earth's surface is the satellite? (Use ratio and proportion.

b) Determine the magnitude of the gravitational force on the satellite.

I know for b) i need a) but i dont seem to get the right answer for a.

for a this is wat i do.

gs=GMs/Rs^2
ge=GMe/Re^2

then i get g s/g e = Ms/Me x (Re/Rs)^2
But i dont get the right answer for it.
 

Answers and Replies

  • #2
2,210
1
You dont need (a) for (b).

For (a) you are given the acceleration due to gravity (the local g) and need to find the distance between earth and the satelite.. just use the equation you have to find the distance..
 
  • #3
Fermat
Homework Helper
872
1
F.B said:
...
for a this is wat i do.
gs=GMs/Rs^2
ge=GMe/Re^2
then i get g s/g e = Ms/Me x (Re/Rs)^2
But i dont get the right answer for it.
The g-value doesn't depend on the mass of the object experiencing the force. It varies due to the distance between the two masses only.

The gravitational force of attraction is given by,

[tex]F = \frac{GMm}{r^2}[/tex]

The gravitational field strength, as you put it, is given by,

[tex]g = \frac{F}{m} = \frac{GM}{r^2}[/tex]

Considering your problem,

[tex]g_s = \frac{GM_e}{r_s^2}[/tex]
[tex]g_e = \frac{GM_e}{r_e^2}[/tex]
[tex]\frac{g_s}{g_e} = \frac{GM_e}{r_s^2} \div \frac{GM_e}{r_e^2}[/tex]
[tex]\frac{g_s}{g_e} = \frac{r_e^2}{r_s^2}[/tex]

Use the above expression to get the height of the satellite above the earth's surface, circa 3,000 km
 
Last edited:

Related Threads on Gravitational Fields

  • Last Post
Replies
1
Views
913
  • Last Post
Replies
2
Views
1K
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
2
Views
642
  • Last Post
Replies
2
Views
812
  • Last Post
Replies
23
Views
2K
  • Last Post
Replies
2
Views
511
  • Last Post
Replies
4
Views
603
Replies
0
Views
2K
  • Last Post
Replies
2
Views
1K
Top