A bullet weighing 9g moves at a speed of 800m / s, pierced the board and flew out of the board at a speed of 200m / s.

A bullet weighing 9g moves at a speed of 800m / s, pierced the board and flew out of the board at a speed of 200m / s. Determine the thickness of the board if the average resistance force acting on the bullet in the board is 108kN

m = 9 g = 0.09 kg.

V1 = 800 m / s.

V2 = 200 m / s.

F = 108 kN = 108000 N.

S -?

The thickness of the board S is the path of the bullet along which it moves at uniform acceleration.

When braking with constant acceleration, and the path S of the bullet is determined by the formula: S = (V1 ^ 2 – V2 ^ 2) / 2 * a.

The acceleration of a bullet a, according to Newton’s 2 law, is directly proportional to the force F, which acts on the bullet, and is inversely proportional to the mass of the bullet m: a = F / m.

The formula for determining the thickness of the board will take the form: S = (V1 ^ 2 – V2 ^ 2) * m / 2 * F.

S = ((800 m / s) ^ 2 – (200 m / s) ^ 2) * 0.009 kg / 2 * 108000 N = 0.025 m.

Answer: the thickness of the board that the bullet pierced is S = 0.025 m.