5 Two particles \(A\) and \(B\) move in the same vertical line. Particle \(A\) is projected vertically upwards from the ground with speed \(20 \mathrm {~m} \mathrm {~s} ^ { - 1 }\). One second later particle \(B\) is dropped from rest from a height of 40 m .

1. Find the height above the ground at which the two particles collide.
2. Find the difference in the speeds of the two particles at the instant when the collision occurs.