Krakow to Warsaw
 

Would it be feasible to do a day trip to Warsaw from Krakow? Should we drive or take the train?

It's 2:39 one way by train. Your call whether that makes it a day trip.

there is now way to make it 1 day trip.

If you'd said Warsaw to Krakow for a day- I would have said NO,but I am sure you could do Warsaw if you went early in the morning and returned late. Take the train. You won't have time for museums,but if you take a guided tour you will see most of the interesting sights of the city. Make sure you sit on a terrace in the Old Town Square for lunch.

Schedules are on www.bahn.de.
Leaving Krakow at 0900, you'd get to Warszawa Centralna at 1145. The trains run hourly. The last one back is at 2005, getting to Krakow at 2250, so you could have eight hours in Warszawa.