A bullet of mass 10g moving horizontally with a
velocity of 400 ``ms^{-1}`` strikes a wooden block of mass
2 kg which is suspended by a light inextensible string
of length 5 m. As a result, the centre of gravity of
the block is found to rise a vertical distance of
10 cm. The speed of the bullet after it emerges out
horizontally from the block will be :-
(1) 120 ``ms^{-1}``
(2) 160 ``ms^{-1}``
(3) 100 ``ms^{-1}``
(4) 80 ``ms^{-1}``