A hammer of mass 100 kg falls 4 metres on to a pile of mass 300 kg and drives it 80 mm into the ground. Using the principle of the conservation of Momentum and D'Alembert's principle:

1. Calculate the kinetic energy of the hammer on impact.
2. Calculate the initial velocity of the pile stating any assumptions.
3. Calculate the average resistance to penetration of the ground.
4. Calculate the work done by the ground and comment on the result.