$⇒$ $v = \sqrt {\frac{{rgh}}{l}} $
$ = \sqrt {\frac{{50 \times 1.5 \times 9.8}}{{10}}} = 8.57\,m/s$

$(A)$ $\theta=45^{\circ}$
$(B)$ $\theta>45^{\circ}$ and a frictional force acts on the block towards $P$.
$(C)$ $\theta>45^{\circ}$ and a frictional force acts on the block towards $Q$.
$(D)$ $\theta<45^{\circ}$ and a frictional force acts on the block towards $Q$.
