[onewhippedpuppy]

Force = mass * acceleration. In that equation, gravity is acceleration. That's where you get your increasing velocity.

Power = Work / Time = (Force * Displacement) / Time = Force * Velocity

You are combining a lot of different physics problems into one. What are you actually looking to calculate, and why? Power is frequently misunderstood, from the layman's perspective the use of power is often incorrectly substituted for torque to describe a force. Power is simply the rate of doing work, which is why it takes several calculations to get there.