Any kinetic energy an object has, it has to get first. If you compare the size of satellites with their respective rocket it looks difficult to make an object of any reasonable mass get any significant speed. You can trick a bit with swing by maneuvers, but as far as I understand no man made object makes any more than a little sound at the atmosphere while entering. You could however poison the planet with a nice substance.
On the other hand it might be possible to use a man made satellite to deflect a bigger object so that it crashes into earth. But please do not try this on your home.
A fair point. On the subject of pulling vast quantities of energy from nowhere, does any one country currently possess the knowledge and materials to build a bomb that detonated on the surface could {split the Earth like a grape}/{smash the Earth like an egg}/{dramatic verb the Earth like a metaphorical noun}?
And yes, not something to try in practice with an inhabited location. Perhaps a computer model, at most... actually, there's a thought regarding morbid fascination. I wonder what would be necessary to provide a sufficiently-realistic (uninhabite...
http://neo.jpl.nasa.gov/risk/2012da14.html
http://rt.com/news/paint-asteroid-earth-nasa-767/
Seems like a good opportunity to bring up existential risks. And A friendly reminder that NASA is in fact pretty damned important.
Thoughts?