I can not solve this problem to save my life

[Sunnie]

An astronaut on the surface of Mercury fires a cannon to launch an experiment package, which leaves the barrel moving horizontally. Assume that the free-fall acceleration on Mercury is three eighths that on the Earth.

(a)What must be the muzzle speed of the package so that it travels completely around Mercury and returns to its original location?

(b) How long does this trip around Mercury take?


the formula that I used (4PiR/T^2)

This is a formula that I have I don't know if it is the correct one though. Please if you have any advice I would really appreciate it.

 

[D H]

You haven't used the given fact regarding free-fall acceleration on Mercury. What is the basic formula for centripetal acceleration for circular motion?

 

[Sunnie]

What formula would that be? I have Vf= Vi-AT. Is that the right one?