Homework Help: Weight of object below the Earth's surface.

1. Oct 18, 2014

rrosa522

1. The problem statement, all variables and given/known data

Calculate the gravitational force acting on a 9.6-kg mass....?
1.5 x 10^4 m above Earth's center. How do i solve this??
2. Relevant equations

3. The attempt at a solution
the answer is 17N but i dont understand how

2. Oct 18, 2014

Staff: Mentor

Hi rrosa522. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif [Broken]

What is the equation for gravitational force between m1 and m2 spaced a distance r apart? If not in your text book, use google.

Last edited by a moderator: May 7, 2017
3. Oct 18, 2014

SteamKing

Staff Emeritus
This chap Isaac Newton had stuff like this figured out.

4. Oct 18, 2014

_N3WTON_

5. Oct 18, 2014

_N3WTON_

try and use this equation:
$F_{grav} = \frac{Gm_{1}m_{2}}{r^2}$
Where m1 and m2 are two masses, r is a distance and G is a constant

6. Oct 18, 2014

rrosa522

i tried the formula but i dont get 17N

7. Oct 18, 2014

_N3WTON_

you should have the mass of earth (its probably in your textbook) we can call this m1, the other mass is given to you. You have the distance of the object, so enter these values into the formula given above

Last edited: Oct 18, 2014
8. Oct 18, 2014

_N3WTON_

Better yet, show me what you are entering in the formula

9. Oct 18, 2014

Staff: Mentor

A distance of 1.5 x 10^4 m from the Earth's center is well below the Earth's surface, and within the inner core. How did you apply Newton's gravitational force law for that location? Show your work.

Also, your thread title does not meet Physics Forums requirements; thread titles should be descriptive of the thread content, describing the problem or area of physics involved. Please note this for future questions that you post. I have changed the title to be more appropriate.

10. Oct 18, 2014

_N3WTON_

I'm sorry, I read the problem as 1.5x10^4 from the earth's surface....either way show how you are using the formula

11. Oct 18, 2014

rrosa522

(6.67x10^-11) (9.6) (5.97 x 10^24) /
(1.5 x 10^4)^2
the answer i get 1.70x10^7 N
(sorry i didnt add units in my solution, its just gets confusing for me)
the answer at the the back of my textbook is 17 N, i don't understand why

12. Oct 18, 2014

rrosa522

(6.67x10^-11) (9.6) (5.97 x 10^24) /
(1.5 x 10^4)^2
the answer i get 1.70x10^7 N
the answer at the the back of my textbook is 17 N, i don't understand why

13. Oct 18, 2014

Staff: Mentor

The textbook is wrong if the radius that you specified is correct.

17 N would be correct if the given radius was in km not meters. That would place the 9.6 kg object well above the Earth's surface. Check the units on the given radius.

14. Oct 19, 2014

hafiz ns

let take one object as earth and other as the object
there distance as 1.5 x 10^4
f=gM1m2/d^2