A bullet of mass m traveling horizontally at a very high speed v embeds itself in a block of mass M that is sitting at rest on a nearly frictionless surface. What is the final speed vf of the block-bullet system after the bullet embeds itself in the block?

Explanation:

Given that

mass of the bullet = m

Speed of the bullet = v

mass of the block = M

Initial speed of the block = 0

The final speed of the bullet and block combine = vf

As we know that ,if external force on the system is zero then the linear momentum of the system will remain conserve.

Pi= Pf

So by using linear momentum conservation

m v + M x 0 = (M+m) vf

m v = (M+m) vf

Therefore the final spped of the system will be

d.7.5cm is your answer