Unfortunately you're being down voted, but the reality is there are crumple zones built into some hoods (bonnets) that help protect the pedestrian from immediately impacting the solid parts of the engine. So the concept isn't completely unexplored.
Airbags and seatbelt pre-tensioners have "explosives" in them (they convert very rapidly into gas, but I'm not sure all of them always meet the usual standards of explosives).
The defective Tanaka airbags used ammonium nitrate, of Oklahoma City Bombing and Beirut port fame.
They wanted to keep the profile of the car low which didn't allow for the space normally needed, so they provide it 'on demand' in case of impact. Unfortunately for a friend of mine who is an owner, that turned a fairly minor collision with an object into a several thousand pound repair as the system shears the bonnet mounts and deforms the bonnet.
