A bullet weighing 10 g flies at a speed of 500 m / s and penetrates a 2 cm thick board. In this case

A bullet weighing 10 g flies at a speed of 500 m / s and penetrates a 2 cm thick board. In this case, the speed of the bullet decreases to 300 m / s. What is the average drag force when the bullet moves in the board?

Data: m (bullet mass) = 10 g = 0.01 kg; V1 (bullet speed before the board is pierced) = 500 m / s; h (board thickness, bullet path) = 2 cm = 0.02 m; V2 (bullet velocity after breaking through the board) = 300 m / s.

To calculate the average resistance force of a taken board, we use the equality: m * V1 ^ 2/2 – m * V2 ^ 2/2 = A = Fcopr * h, whence Fcopr = m * (V1 ^ 2 – V2 ^ 2) / (2 * h).

Calculation: Fcopr = 0.01 * (500 ^ 2 – 300 ^ 2) / (2 * 0.02) = 40 * 10 ^ 3 N (40 kN).

Answer: The average resistance force is 40 kN.