# Homework Help: Acceleration due to gravity

1. Nov 14, 2004

### cougar_21

Ok, please tell me if i am correct, or totally out of it

What is the acceleration due to gravity on the surface of
(a) the Moon (R=1.74x10^3km, m= 7.35x10^22kg)
(b) Mars (R=3.40x10^3km, m= 6.42x10^23kg)

i used v= square root of m/R

for a i got 6.4993x 10^9
for b i got 1.3741 X 10^10

is this correct, cause i really am not confident :rofl:

2. Nov 14, 2004

### cougar_21

k i took a different approach please tell me which one is the correct one:
this time i took Gm/R^2 to get the acc.

for a i got 1.62 m/s^2
o.0 sorry i really have no clue what I am doing

Last edited: Nov 14, 2004
3. Nov 14, 2004

### CartoonKid

You should use the second one. Basically, they are all originated from $$\frac{GMm}{R^2}$$. You got the first one by equalling it to centripedal force and the second to $$mg$$.

4. Nov 14, 2004

### cougar_21

k so then the second equation is the correct one? TY

Another question since the R is in km should I change it to meters?

Last edited: Nov 14, 2004
5. Nov 14, 2004

### CartoonKid

Yes, you have to change them to SI unit.

6. Nov 14, 2004

### Janus

Staff Emeritus
yes, you should.

7. Nov 16, 2004

thank you !!