6.
\begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{82cadc37-4cb0-455e-9531-e09ec0c19533-11_711_917_219_561}
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\caption{Figure 4}
\end{figure}
A particle \(P\) is projected from a point \(A\) with speed \(25 \mathrm {~m} \mathrm {~s} ^ { - 1 }\) at an angle of elevation \(\alpha\), where \(\sin \alpha = \frac { 4 } { 5 }\). The point \(A\) is 10 m vertically above the point \(O\) which is on horizontal ground, as shown in Figure 4. The particle \(P\) moves freely under gravity and reaches the ground at the point \(B\).
Calculate
- the greatest height above the ground of \(P\), as it moves from \(A\) to \(B\),
- the distance \(O B\).
The point \(C\) lies on the path of \(P\). The direction of motion of \(P\) at \(C\) is perpendicular to the direction of motion of \(P\) at \(A\).
- Find the time taken by \(P\) to move from \(A\) to \(C\).