Answer: The velocity of concrete block is 0.353 m/s
Step-by-step explanation:
To calculate the velocity of the concrete block after the collision, we use the equation of law of conservation of momentum, which is:

where,
= mass of rubber bullet = 0.012 kg
= Initial velocity of rubber bullet = 150 m/s
= Final velocity of rubber bullet = -100 m/s
= mass of concrete block = 8.5 kg
= Initial velocity of concrete block = 0 m/s
= Final velocity of concrete block = ?
Putting values in above equation, we get:

Hence, the velocity of concrete block is 0.353 m/s