Two blocks are travelling towards eachother. The first has a speed of 10cm/sec and the second has a speed of 60 cm/sec. after the collison the second is observed to be travelling with a speed of 20 cm/sec in a direction opposite to its initial velocity. if the weight of the first block is twice that of the second, determine:
a) the velocity of the first block after collision;
b) whether the collision was elastic or in elastic.