Answer:
1.67 m/s
Step-by-step explanation:
Since this is an inelastic collision (the block and the arrow stick together after the collision), we can solve the problem by using the law of conservation of momentum:

where
is the mass of the arrow
is the initial speed of the arrow
is the mass of the block
is the initial speed of the block
is the final speed of the arrow+block
Substituting and re-arranging the equation, we find:
