Bullet imbedding in a block on a frictionless surface

[Dustinsfl]

A 10g bullet with v = 1000 m/s strikes a 100g block which is at rest. What is their combined velocity? Can this be done with conservation of energy? momemtum?

Here we have inelastic collision so by conservation of momentum
\[
10\cdot 1000 + 0 = 110\cdot v_f\Rightarrow v_f = \frac{1000}{11}m/s.
\]
Can this be done with CoE? If so, how?

 

[Ackbach]

Re: bullet imbedding in a block on a frictionless surface

A 10g bullet with v = 1000 m/s strikes a 100g block which is at rest. What is their combined velocity? Can this be done with conservation of energy? momemtum?

Here we have inelastic collision so by conservation of momentum
\[
10\cdot 1000 + 0 = 110\cdot v_f\Rightarrow v_f = \frac{1000}{11}m/s.
\]
Can this be done with CoE? If so, how?

No, it cannot, because the collision is inelastic. An elastic collision, by definition, is a collision in which kinetic energy is conserved. With an inelastic collision, it is not conserved. Moreover, you're given no information about the force during the collision, so you can't use Newton's Second Law, or a more general conservation of energy approach. Conservation of Momentum is all that's available to you.