# Homework Help: A question that asks you to figure out the mass of the moon

1. Jan 25, 2012

### Hmpca

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

the radius of the moon is 1 over 3.65 of the radius of the earth, while the acceleration due to gravity of the moon is 1 over 6 of that on the earths surface. calculate the mass of the moon.

2. Jan 25, 2012

### PeterO

The acceleration due to gravity - we call it g on Earth - is given by GM/R2. Where G is the universal constant of gravitation; M is the mass of the central body; and R is the distance form the centre of mass - the radius of the body if we consider g on the surface. You know sufficient of those values to calculate the mass of the Moon as a fraction of the mass of the Earth, which is a value that can be looked up easily.

3. Jan 25, 2012

### Hmpca

i thought you could figure out the mass of the moon without knowing the mass of the earth. tomorrow i have an exam and my teacher said dont expect me to give you any sheet with equations and constants. so i guess i got to memorize the mass of the earth.
thank you

4. Jan 25, 2012

### homevolend

a = GM/R2

g = (1/6)(9.81) = X m/s2

r = (1/3.65)(6.378x106) = Y m

m/r2 = a/G

m/(Y)2 = X/ (6.67x10-11)

m = ANS kg

5. Jan 25, 2012

### netgypsy

the person asking for help is supposed to set up the problem, give relevant equations etc. before getting help from outside. Where are your equations??

In answer to your question - you do have to know the formulas probably but not the mass of the earth.