6 A block of wood of mass 2 kg is suspended by long, light strings and is at rest. A bullet of mass 40 g, strikes and remains in the block, causing it to swing. The maximum height of the block above its rest position is 51 cm. Find:
a) the kinetic energy of the bullet plus block immediately after impact;
b) the velocity of the bullet at impact
c) the kinetic energy of the bullet at impact.
Why are the answers to a) and c) not equal?