The bullet, having pierced the board, reduced its speed by half. How many percent of its initial kinetic energy

The bullet, having pierced the board, reduced its speed by half. How many percent of its initial kinetic energy was converted into heat and deformation energy?

Data: V1 (speed of the bullet before piercing the board) = 2V2 (speed at the exit from the board).

To find the percentage of the initial kinetic energy of a given bullet, converted into deformation energy and heat, we use the ratio: η = 1 – Ek2 / Ek1 = 1 – 0.5 * m * V2 ^ 2 / (0.5 * m * V1 ^ 2 ) = 1 – V2 ^ 2 / 4V2 ^ 2 = 1 – 0.25 = 0.75 or 75%.

Answer: 75% of the initial kinetic energy of a given bullet passed into the deformation energy and heat.