# Gravity/Circular Motion

hey, i am really stuck on this problem and i was wondering if anyone could help me...

The planet Mercury orbits the Sun at a mean distance of 5.80X10^7 km.
a) calculate the strength of the Sun's gravity field (g) at Mercury's mean distance.
b) Calculate Mercury's orbital speed in m/s and in km/h.

Any assistance on the problem would be greatly appreciated!!

Related Introductory Physics Homework Help News on Phys.org
ranger
Gold Member
Hi vasfinest18,

In the future, post questions like these in the homework section. And lastly, you must show an attempt. So any thoughts what to do?

is the formula that i need to use g=GM/r^2??? there must be some more info that i need to derive from the problem, because i was only given 1 number. should i substitute 10m/s^2 in for G?? but if that is the right equation to use, i am still missing another piece of info that i would need...

## Homework Statement

The planet Mercury orbits the Sun at a mean distance of 5.80X10^7 km.
a) calculate the strength of the Sun's gravity field (g) at Mercury's mean distance.
b) Calculate Mercury's orbital speed in m/s and in km/h.

## Homework Equations

g=GM/r^2... i think but i need 3 out of those 4 variables, and i only have 1 given.. G is mostly likely 10 m/s^2, but from there i dont know how to calculate 'g' or M.

## The Attempt at a Solution

ranger
Gold Member
Well for first problem, you are right track. G is simply the gravitational constant (look up the value). r is the distance between the sun and mercury. And you already know the mass of the sun. Just plug in the values into the formula and all should be good.

Pyrrhus
Homework Helper
Open your physics book, there you will find the values you don't have. Usually on a table.

is the mean distance the radius? and for the mass should i just look up the mass of the sun?

ranger
Gold Member
is the mean distance the radius? and for the mass should i just look up the mass of the sun?
The planet Mercury orbits the Sun at a mean distance of 5.80X10^7 km.
Obviously you must look up the mass if you do not know it.

ZapperZ
Staff Emeritus
If this thread appears to be confusing, that's because it has been merged with another that was posted in the wrong forum.

Zz.

I dont find this thread constructive at all.
The question is blatantly straightforward.

g=GM/r²
where g = gravitational strength at that point,
G = gravitational constant,
M = mass of the object "creating" the gravity field, the sun in this case,
r = distance between the CG(center of gravity) sun and CG of the planet.