A bullet of mass $5g$ moving with an initial

speed $400\frac{m}{s}$ is fired into and passes through

a block of mass $7kg,$ as shown in the figure.

The block, initially at rest on a frictionless,

horizontal surface, is connected to a spring of

force constant $431\frac{N}{m}.$

If the block moves a distance $1\mathrm{.}3cm$ to the

right after the bullet passed through it$,$ find

the speed $v$ at which the bullet emerges from

the block.

Answer in units of $\frac{m}{s}.$

part $2$ of $2$

Find the magnitude of the energy lost in

the collision.

Answer in units of $J.$