Question

A thin block of soft wood with a mass of 0.078 kg rests on a horizontal frictionless surface. A bullet with a mass of 4.67 g is fired with a speed of 601 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 (in m/s) 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 energy less 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 in joules.

KEi =

KEf =

Answer 1

The initial part of the problem is a conservation of momentum problem. The initial momentum of the system should be equal to the final momentum. Since the initial velocity of the block is zero, the initial momentum of the system is only due to the bullet. The final momentum of the system will be the sum of the final momenta of the bullet and the block.

Part A- final speed of the bullet.

Therefore, the final velocity of the bullet is

Part B

Since energy will be lost in penetrating the block, the final kinetic energy of the system will be less than the initial kinetic energy.

Part C

Here, we can see that the final kinetic energy is less than the initial kinetic energy.