# Homework Help: Acceleration in a vacuum

1. Jul 4, 2006

### uwmphysics

Ok the question I have is pretty simple

we claimed thatif the air resistance could be neglected all objects on hte moon wuld fall at
a. the same constant speed
b. an increasing acceleration
c. the same constant acceleration
d. a decreasing acceleration

Ok so i know its not the same constant speed, because the acceleration is what changes. And I know the acceleration isnt decreasing, or it would be getting slower and stop mid air...which obviously doesnt happen. So I'm torn between b and c, an increasing acceleration and the same constant acceleration. If we use the rule that gravity pulls us 10 m/s-squared then it would have the same acceleration the whole time and the velocity would increase, so the answer has to be c right?

...ok now that i'm confused hopefully someone agrees with me or can explain why thats wrong.

2. Jul 4, 2006

### Staff: Mentor

As long as we are only talking about objects near the moon's surface, then they all fall with the same acceleration--for the same reason that falling objects near the Earth's surface all have the same acceleration (ignoring air resistance). The acceleration due to gravity near the Earth's surface is about 10 m/s^2. Would you expect the acceleration due to gravity on the moon to be the same? smaller? greater?

3. Jul 4, 2006

### Kurdt

Staff Emeritus
I agree with you. That is assuming that the object is at small distances wrt the moons radius.

EDIT: Beaten to it by a better explaination.