THANK YOU FOR MAKING ANSWERS CLEAR SO I CAN RATE YOU ACCORDINGLY, WHEN I GET A C

Question

THANK YOU FOR MAKING ANSWERS CLEAR SO I CAN RATE YOU ACCORDINGLY, WHEN I GET A CHANCE.

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 625 m/s at a block of wood and passes completely through it. The speed of the block is 21 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.

equal to the initial kinetic energyless than the initial kinetic energy    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) As given in the question, the speed of the bullet when it exits the block is 21m/s.
b) The final kinetic energy is lower than that of the initial kinetic energy. This is so as the initial kinetic energy is converted into other forms of energy such as heat energy and sound energy upon hitting the surface of the block of wood.
In the energy equation,
Initial kinetic energy = Heat energy + sound energy + Final kinetic energy

c) Given that the formula of kinetic energy : KE = 0.5mv^2,
Where m is the mass of the bullet and v is the velocity of the bullet at a given time,
Initial KE = 0.5 (0.00467kg) (625m/s)^2
= 912.10 J
Final KE = 0.5 (0.00467kg) (21m/s)^2
= 1.0297 J

Since 912.10 J > 1.0297J, the initial kinetic energy is much greater than that of the final kinetic energy.

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