Gravitational Force

[kevi555]

Hey there,

 

Quick question, any ideas on how to solve would be greatly appreciated.

 

Q: At a distance 'H' above the surface of a planet, the true weight of a remote probe is one percent less than its true weight on the surface. Find the ratio H/R.

 

Thanks all.

 

Kev

[timo]

Weight F as a function of distance r from the center of the planet goes as F ~ 1/r².

[kevi555]

Thanks, could you explain what you mean by F ~ 1/r^2 ?

 

K

[timo]

By that I mean that F = C/r², where C>0 is a constant which will cancel out in your case. Therefore, it´s exact value is irrelevant. However if this is homework, it might be better using the full term for F (the force due to gravity) because showing that everything except the dependence on r cancels out might be part of the assignement. Here´s the full term: http://en.wikipedia.org/wiki/Gravity#Newton.27s_law_of_universal_gravitation

[kevi555]

Alright, and finally how can you find a ratio from that and use 0.99 ( for 99%)?

 

Yes, it's for homework. I appreciate your help too.

[swansont]

Write down the equations for the weight for the two situations, in terms of H and R. Take the ratio, and solve for 0.99. Rearrange in terms of H/R