A 5.00 g bullet moving with an initial speed of 450 m/s is fired into and passes through a 1.00 kg block, as in Figure P9.67. The block, initially at rest on a frictionless, horizontal surface, is connected to a spring of force constant 985 N/m.

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anonymous · Answer

I don't see the figure, but you are probably asked to find the deflection of the spring.
 Bullet kinetic energy, (1/2) m v^2 will become compressed spring potential energy (1/2) k x^2.