4. In this question use \(g = 9.81 \mathrm {~m} \mathrm {~s} ^ { - 2 }\)
A particle is projected with an initial speed \(u\), at an angle of \(35 ^ { \circ }\) above the horizontal.
It lands at a point 10 metres vertically below its starting position.
The particle takes 1.5 seconds to reach the highest point of its trajectory.
Find \(u\).