A thin block of soft wood with a mass of 0.070 kg rests on a horizontal friction

Question

A thin block of soft wood with a mass of 0.070 kg rests on a horizontal frictionless surface. A bullet with a mass of 4.67 g is fired with a speed of 577 m/s at a block of wood and passes completely through it. The speed of the block is 16 m/s immediately after the bullet exits the block.

(a) Determine the speed of the bullet as it exits the block in m/s.

(b) Determine if the final kinetic energy of this system (block and bullet) is equal to, less than, or greater than the initial kinetic energy.

less than the initial kinetic energy - correct

(c) Verify your answer to part (b) by calculating the initial and final kinetic energies of the system in J.

Explanation / Answer

a)Conserving momentum.

mu=Mv+mv2

0.00467*577=0.07*16+0.00467*v2

v2=337.2m/s

c) Initial KE=0.5*0.00467*577^2=777.4J

Final KE=0.5*0.00467*337.2^2+0.5*0.07*16^2=274.5J

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