If your anchored-to-a-gateway-at-one-end-but-other-end-free-floating wormhole technology has the handwaved ability to match orientation and velocity to the surface of a distant planet, it also has the ability to not match the orientation and velocity of the surface of a distant planet, and if you configure it to be, say, facing downwards and descending vertically at 5km/s, then you have the delivery mechanism for a kinetic bombardment: launch a tungsten slug through the wormhole carefully timed to pass through just as the wormhole approaches the ground, then cut or divert the gateway so you don't get too much shrapnel back through on your side.
One downside to this is that while your wormhole-cannon is firing, it's scooping up a cylinder of the target planet's atmosphere and jetting it back out on your side at the impact velocity. While 5km/s wind in exchange for 5km/s tungsten slug is still an advantageous trade, what sort of damage might you expect such a wind to do on your side? What sort of protective measures would you want to put in place around your gateway buildings to prepare for this 'recoil'?
Assume the gateway is 10m diameter, probably outside on a large hardstanding area (airport runway style). I'm imagining launching the slug on a missile from some distance, since it needs to have enough momentum to travel 'upwind' to the gateway. Total firing time would be 5-10s.
Edit: changed the impact velocity from 20km/s to 5km/s, to be within range of current hypervelocity weapons.