# Acceleration due to gravity help

1. Jun 14, 2008

### sheevz

acceleration due to gravity help!!

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

PROB: How long would it take for a mass of 1kg to fall a distance of 2m to the surface of the moon?

2. Relevant equations

G=6.673*10^-11 Nm^2/kg^2
R of moon = 1.76*10^6m
m of moon = 7.35*10^22kg

3. The attempt at a solution
i started by finding the acceleration due to gravity by using g= (m)(G)/r^2
(m=mass of moon, G as the gravitational constant, r= radius of moon)
finding that g is 1.58m/s^2
now i am lost in what formula to use to get the displacement of this object???

2. Jun 14, 2008

### konthelion

Check your acceleration due to gravity for the moon, it should be ~1.62m/s^2

To solve for time t, use the formula $$x=v_{0}t+\frac{1}{2}at^2$$

3. Jun 14, 2008

### sheevz

ok i dont know if this is a type o or not but yes the acceleration due to gravity for the moon is ~1.62m/s^2 but in this prob, the radius is given @ 1.76*10^6 thus giving an acceleration due to gravity @ ~1.58m/s^2
and in using the above formula you gave me, X=Vot+.5at^2
is Vo my accel due to gravity on the moon and a my G constant? why in the original problem was G given to me, is it necessary in this? (probably a stupid question)

4. Jun 15, 2008

### Gib Z

Those pieces of data were given to you so you could work out the acceleration due to gravity, to sub into the formula konthelion gave to you. Obviously you did this through Newtons Universal Law of Gravitation. After we have the force, Using Newtons Second Law we can have the acceleration. We can take the Force and acceleration to be practically constant, because the change in the value of r in the Universal Gravitation Law changes by one 1m, very small in comparison to the radius of the moon. Although yes, it is true it is not exactly constant.