A thin block of soft wood with a mass of 0.082 kg rests on a horizontal friction

Question

A thin block of soft wood with a mass of 0.082 kg rests on a horizontal frictionless surface. A bullet with a mass of 4.67 g is fired with a speed of 607 m/s at a block of wood and passes completely through it. The speed of the block is 23 m/s immediately after the bullet exits the block. (a) Determine the speed of the bullet as it exits the block. _____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.

a.)equal to the initial kinetic energy

b.)less than the initial kinetic energy

c.)greater than the initial kinetic energy

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

KEi = ______J

KEf = _____J

Explanation / Answer

(a)  Initial momentum of the system ( block + bullet)

pi = (0.00467) (617)

= 2.834

Final momentum of the system ( block + bullet) = (0.00467) vb + (0.082) (23)

= (0.00467) vb + 1.886 N

the external force acting on the system is zero

thus, momentum of system is conserved  

(0.00467) vb + 1.886 N = 2.834

vb = (0.948) / (0.00467)

= 202.99 m / s

(b)

the final kinetic energy can be calculated from

KE = (1 / 2) m v2

taking the velocity of block or bullet required

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