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I have a satellite orbit problem I'm not quite understanding...any help would be appreciated.

Suppose a spacecraft orbits the moon in a very low, circular orbit, just a few hundred meters above the lunar surface. The moon has a diameter of 3500 km, and the free-fall acceleration at the surface is 1.60 m/s^2.

1. How fast is this spacecraft moving?

To find the speed, I used the equation v= square root of (G X M/R), with M being the mass of the moon (I had to look that up) and G being the gravitational constant.

v= square root of (6.674E-11)(7.36E22/1750)=52980.125=>52.9 m/s

The answer I got was an available option under the answer choices; however, I got it wrong. I can't figure out another way to come up with the velocity.

I also tried using the equation mg=mv^2/R; however, I got the same number as before.

m's cancel;

g=v^2/R

v= square root of g*R

Acceleration = g in freefall

V = square root of 1.60*1750km=>52.9 m/s

Both of these answers are incorrect. What am I doing wrong?

## Homework Statement

Suppose a spacecraft orbits the moon in a very low, circular orbit, just a few hundred meters above the lunar surface. The moon has a diameter of 3500 km, and the free-fall acceleration at the surface is 1.60 m/s^2.

## Homework Equations

1. How fast is this spacecraft moving?

## The Attempt at a Solution

To find the speed, I used the equation v= square root of (G X M/R), with M being the mass of the moon (I had to look that up) and G being the gravitational constant.

v= square root of (6.674E-11)(7.36E22/1750)=52980.125=>52.9 m/s

The answer I got was an available option under the answer choices; however, I got it wrong. I can't figure out another way to come up with the velocity.

I also tried using the equation mg=mv^2/R; however, I got the same number as before.

m's cancel;

g=v^2/R

v= square root of g*R

Acceleration = g in freefall

V = square root of 1.60*1750km=>52.9 m/s

Both of these answers are incorrect. What am I doing wrong?

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