# A bullet flying at a speed of 400 km / h pierced a wall 20 m thick, as a result, the bullet

A bullet flying at a speed of 400 km / h pierced a wall 20 m thick, as a result, the bullet reduced the speed to 100 km / h how much the bullet was moving in the wall.

Task data: V0 (bullet speed before hitting the wall) = 400 km / h (111.11 m / s); S (wall thickness, distance traveled) = 20 m; V (final bullet velocity) = 100 km / h (27.78 m / s).

1) Define the acceleration of the bullet: S = (V ^ 2 – V0 ^ 2) / 2a, whence a = (V2 – V0 ^ 2) / 2S = (27.78 ^ 2 – 111.11 ^ 2) / (2 * 20) ≈ -289 m / s2.

2) Calculate the time of movement of the bullet in the wall: t = (V – V0) / a = (27.78 -111.11) / (-289) ≈ 0.29 s.

Answer: The bullet moved in the wall for 0.29 s.

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