What is the speed of a motionless bar weighing 4 kg if it gets hit by a bullet weighing 20 g, flying horizontally

| September 9, 2021 | education

What is the speed of a motionless bar weighing 4 kg if it gets hit by a bullet weighing 20 g, flying horizontally at a speed of 700 m / s, and gets stuck in it?

mb = 4 kg.

mp = 20 g = 0.02 kg.

Vb = 0 m / s.

Vp = 700 m / s.

Vb “-?

Since the bullet interacts only with the bar, they can be considered a closed system of bodies.

For a closed system of bodies, the law of conservation of momentum is valid: mb * Vb + mp * Vp = (mb + mp) * Vb “, where mb * Vb is the impulse of the bar before the bullet hits, mp * Vp is the momentum of the bullet before it hits the bar, (mb + mp) * Vb “- the impulse of the bullet with the bar after the hit.

The speed of movement of the bar with the bullet after the hit Vb “will be determined by the formula: Vb” = (mb * Vb + mp * Vp) / (mb + mp).

Vb “= (4 kg * 0 m / s + 0.02 kg * 700 m / s) / (4 kg + 0.02 kg) = 3.5 m / s.

Answer: after being hit by a bullet, the bar will move at a speed of Vb “= 3.5 m / s.



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