Strongest Door Stopper, Heavy Duty Door Stop Wedge Made of Premium Quality Zinc and Rubber Suits Any Door, Any Floor. Set of 6

Would these keep a classroom door shut to help deter someone from coming into the room?

Does it come with a self stick holder to hold it on the door/wall when not in use?

Can't someone just reach under the door from the outside and push the door jamber into the room?

Will this work on cement floor? The door stops I have purchased in the past alway slip on the cement flooring so cannot hold the heavy door.