...at constand speed is there a force keeping it in motion?

An object in motion tends to stay in motion. It's one of Newton's laws of motion.

The momentum of the object keeps it moving, but there is drag on the puck at all times. Eventually, the drag coefficient becomes enough to begin slowing the puck, thus slowing the momentus energy, and causing the puck to stop.

no f=maconstant speed means no acceleration, a=0 f must =0

It would never slide at a constant speed... so I guess the question is pointless... or just to see how many people are awake...

I am going to say kinetic energy keeps it going, and lack of resistance, either to the ice, or wind/air allows it to go a long way. But even a puck will loose speed and stop eventually.

The force keeping the puck in motion is gravity and the motion is down. Gravity pulls down on the puck which keeps it in contact with the ice. The ice and air cause drag which slows the puck until it stops.Momentum is the force that keeps the puck moving horizontally until it stops.

i got a couple of answers for you: 1) an object stays in motion unless there is an another force, lesser force (will slow down the object), equal force (will stop the object) or greater force (will counteract the motion of that object). 2) friction-- if there is no friction that will counteract to an object that is in motion, an example of it is when your walking (there is a friction between the sole of your shoes and the ground) or just imagine yourself being pushed in the outerspace without gravity or no grounds to stop you.