Energy transformer

A body of mass 1 kg falls from a height of 1 m. Convert as much as possible of the released potential energy into electrical energy and use that to charge a condenser of 100mF.
This was one of the exercises of the International Young Physicists Tournament in 1999.

From the own built device:

After thinking over a couple of alternatives in theory, we decided to solve the problem with a simple device, using a generator.
We used an AC generator that originally had been an engine of a printer.

We fitted the engine's cogwheel to a rotating axle with a suitable transmission, and just this increased the rpm of the engine functioning as a generator. We fit a pulley to the axle, and we wound a 1 metre long string on it. We put the 1 kg body on the free end of the string.
After letting the body go, the generator began to rotate, and it produced AC. We transformed it to DC to charge the condenser.
The theory was simple, but the building of the device caused much more trouble to us (the fitting of the cogwheel, making the axle); the result was very poor. We had to recognise that the huge part of the potential energy of the body stayed at kinetic energy before hitting the ground, and at the impact, it's wasted. Besides this, the recharging of the condenser is too fast.
We reached a better efficiency by fitting bars at right angles to the axle, and we put weights, onto that bars (the distance of the weights was adjustable). Due to this, the body hit the ground slower, and the most of the potential energy turned into rotation energy This rotation energy -existing after the impact too- continued to charge the condenser. With this method we could charge the condenser even to 110V, and we reached the efficiency of a better steam engine (6%) by trying to place the weights in the most suitable distance from the axle.
During solving the problem, we didn't just have to think over the theory, but we had to put it into practise, and this required very good manual skill. Naturally we were proud of the device.