5 A particle \(P\) is projected vertically upwards, from horizontal ground, with speed \(8.4 \mathrm {~m} \mathrm {~s} ^ { - 1 }\).
- Show that the greatest height above the ground reached by P is 3.6 m .
A particle Q is projected vertically upwards, from a point 2 m above the ground, with speed \(\mathrm { um } \mathrm { s } ^ { - 1 }\). The greatest height abovetheground reached by Q is also 3.6 m .
- Find the value of \(u\).
It is given that P and Q are projected simultaneously.
- Show that, at the instant when P and Q are at the same height, the particles have the same speed and are moving in opposite directions.