# Gravitational Acceleration-Orbital Motion

## Homework Statement

The weight of a 0.60 kg object at the surface of Planet V is 20 N. The radius of the planet is 4 x 10^6 m. Find the gravitational acceleration at a distance of 2 x 10^6 m from the surface of this planet.

a. 8.9 m/s2
b. 11 m/s2
c. 13 m/s2
d. 18 m/s2

F=ma
a=MG/r^2

## The Attempt at a Solution

I did
acceleration at surface=20N/.6kg=33.33m/s^2
acceleration at surface=MG/r^2
MG=33.33m/s^2*(4x10^6)^2

acceleration at a distance=MG/(r+d)^2
a at a distance=(33.33m/s^2*(4x10^6)^2)/(2x10^6+4x10^6)^2
a=14.8m/s^2 which is not in the options

## Answers and Replies

I can't see anything wrong with your method. I did exactly the same and got the same answer as you !!!!
It will be interesting to see if there are any other responses to your posting.

phyzguy
Science Advisor
I think you did it right and the question is wrong. Anyone else see an error?

I get 8.89...

The weight will be 8.89N

Settled! Answers wrong

phyzguy
Science Advisor
It doesn't ask for the weight, it asks for the acceleration, which should be 14.8 like the OP calculated.

thanks :D