A pile driver of mass 500 kg is allowed to fall from rest through a distance of 1.8 m on to a 200 kg concrete pile to drive it into the ground.Each impact drives the pile into the ground by a further 150 mm. Assuming that the pile driver remains in contact with the pile after impact and that momentum is conserved, use the principle of conservation of energy to calculate:

1. The kinetic energy of the driver and pile combination immediately after impact.
2. The change in potential energy of the driver and pile combination on moving into the ground.
3. The average retarding force that brings the pile and driver to rest, ensuring use of the principle of conservation of energy.
4. Using D'Alembert's principle, solve the same problem specified in Task 6c.
5. Compare and contrast the use of the 'principle of conservation of energy' and 'D'Alembert's principle' for solving this problem.

(Assume acceleration due to gravity g=9.81m/s²)