A 5.00 g bullet, moving with an initial speed of 400 m/s, is fired and passed through a 1.00 kg block, as shown in the figure. The block, initially at rest on a horizontal surface without friction, is connected to a spring with a constant force of 900 N/m. The block moves 5.00 cm to the right after impact. Find a) how quickly the bullet leaves the block and b) the mechanical energy that becomes internal energy in the collision.

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