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17. A cubical block of side a moving with velocity v on a horizontal smooth the plane as shown in figure. It hits a ridge at point O and starts rotating about the edge in contact with O. The angular speed of the block after it hits O is 

$$\begin{gathered} \text{(1) }\frac{\text{3v}}{\text{4a}} \\ \text{(2) }\frac{\text{3v}}{\text{2a}} \\ \text{(3) }\sqrt{\frac{3}{2}}\frac{\text{v}}{\text{a}} \\ \text{(4) Zero} \end{gathered}$$