How do I physics Run

how do i make object to run X position with physics?? and increase or decrease speed with how fast press Space Bar? and when no space bar hit start decrease speed slow. oO

On 'space' pressed

Apply physics force to the angle you need.

If the thing is flying, it stops because of the Linear damping. Start at 0.6 ? Start with a force of 80 ? Tweak as you like.

What you created now is like falling in the atmosphere. Gravity applies a continuous force. Air damps. That also means that there will be a (approached) max speed.

If the thing is not flying but standing on another (immovable) physics object. It is the friction of both objects that damp. So, same method, but tweak the friction of both objects to you liking.