4 A particle \(P\) is projected vertically upwards from horizontal ground with speed \(12 \mathrm {~m} \mathrm {~s} ^ { - 1 }\).
- Find the time taken for \(P\) to return to the ground.
The time in seconds after \(P\) is projected is denoted by \(t\). When \(t = 1\), a second particle \(Q\) is projected vertically upwards with speed \(10 \mathrm {~m} \mathrm {~s} ^ { - 1 }\) from a point which is 5 m above the ground. Particles \(P\) and \(Q\) move in different vertical lines. - Find the set of values of \(t\) for which the two particles are moving in the same direction.