Yes to the action, no to the bolded part. You'd still have the same momentum. You'd need to "spend" that somehow. As written above, you'd reduce the falling damage from 50ft worth to 20ft worth. Have the misty step spit you out going up from the ground and you'd still have momentum carrying you up into the air...only to fall back down. Again, you'd reduce the falling damage but not negate it.For example, on your turn you use movement to jump off of a 50 foot cliff. Then after you have dropped 20 feet you use misty step to misty step to the ground and land without taking any falling damage.
Would you allow this?
Why? Obviously I can choose the alignment of the exit of my teleportation. If I've fallen 20ft, and I come out aimed upward at a 45 degree angle, I can't imagine taking more than a single d6, at most.Yes, you can do it. Yes, you'll take 2d6 damage for the 20ft falling not covered by misty step.
Exactly. In my group, the number one rule is "don't let rules hold back the game".I like @doctorbadwolf 's position where the caster decides if momentum is conserved or not. I would also say that since this is essentially using a 2nd level spell slot for a worse featherfall (since it only effects you), then I don't mind increasing the utility of Misty Step in this way.
And if momentum is conserved then a teleportation linear accelerator planet killer system is also possible.if momentum is not conserved, teleportation spells would be lethal, as we are currently moving at VERY high speed around the sun etc.