Gravitational Potential Energy of the earth

Click For Summary
To determine how high above Earth's surface a mass must be for its gravitational potential energy to be 17% of its surface value, the equation PEg = (-GMm)/r is used. The user initially set r1 to 1 meter, leading to confusion as it did not yield a sensible height. Clarification was provided that the radius of Earth is significantly larger than 1 meter, which is crucial for accurate calculations. By correctly applying the Earth's radius, the user was able to arrive at the right answer. Understanding that gravitational potential energy approaches zero at infinity is also an important aspect of the problem.
kt102188
Messages
3
Reaction score
0

Homework Statement



How high above the surface of the Earth must a mass be located so its gravitational potential energy is only 17.00% of its value on the surface?


Homework Equations



PEg=(-GMm)/r, PElocal= mgy where y is height the object can fall

The Attempt at a Solution



I've tried a couple of different things but all my variables cancel out.

(-GMm)/r1=0.17((-GMm)/r2

r1/0.17=r2 If I randomly set r1 to be 1 r2= 5.88235 but that doesn't make sense because if you raise an object by 5m it would have a greater PEg

Any suggestions on where to go?
Thanks!
 
Physics news on Phys.org
Welcome to PF!

Hi kt102188! Welcome to PF! :smile:
kt102188 said:
r1/0.17=r2 If I randomly set r1 to be 1 r2= 5.88235 but that doesn't make sense because if you raise an object by 5m it would have a greater PEg

But the radius of the Earth is a lot larger than 1m. :confused:

(and remember, the question assumes that the PE at ∞ is zero :wink:)
 
Thank you! I was totally thinking of this wrong. Actually using the radius of Earth got the right answer.
 

Thread 'Magnitude of buoyant force in fluids of different densities'

The book claims the answer is that all the magnitudes are the same because "the gravitational force on the penguin is the same". I'm having trouble understanding this. I thought the buoyant force was equal to the weight of the fluid displaced. Weight depends on mass which depends on density. Therefore, due to the differing densities the buoyant force will be different in each case? Is this incorrect?
View full post »

Similar threads

Variation of escape velocity with equal surface gravity
  • · Replies 7 ·
Replies
7
Views
1K
Is potential energy defined only for internal conservative forces?
  • · Replies 15 ·
Replies
15
Views
2K
Gravitational Potential Energy questions near the surface of a planet
  • · Replies 8 ·
Replies
8
Views
2K
Gravitational potential energy
  • · Replies 3 ·
Replies
3
Views
1K
Potential Energy and raising a satellite from Earth into a Circular Orbit
  • · Replies 5 ·
Replies
5
Views
3K
Conservation of Energy with Gravitational Potential Energy
  • · Replies 6 ·
Replies
6
Views
2K
Gravitational potential energy traveling from earth to mars
  • · Replies 7 ·
Replies
7
Views
3K
Integral for work done leading to potential energy sign confusion
  • · Replies 5 ·
Replies
5
Views
2K
Change in Potential Energy levels of a body in Gravitational field.
  • · Replies 9 ·
Replies
9
Views
5K
Elliptical orbit/ determine speed & potential energy
  • · Replies 1 ·
Replies
1
Views
1K