A bullet with a mass of 10 imbeds itself in a wooden block of mass 3990g and is free to move. If the speed of the block and bullet together is 50 cm/s just after the impact what was the original speed of the bullet ?
Use conservation of momentum:
m1*v1 = m2*v2
Where m1 and v1 are the mass and speed of the initial system, m2 and v2 are the mass and speed of the final system
10*v1 = (10+3990)*50