A knife thrower throws a knife toward a 300 g target that is sliding in her direction at a speed of 2.45 m/s on a horizontal frictionless surface. She throws a 22.5 g knife at the target with a speed of 36.0 m/s. The target is stopped by the impact and the knife passes through the target. Determine the speed of the knife (in m/s) after passing through the target.

Question

Physics

Mckee

14 October, 21:25

A knife thrower throws a knife toward a 300 g target that is sliding in her direction at a speed of 2.45 m/s on a horizontal frictionless surface. She throws a 22.5 g knife at the target with a speed of 36.0 m/s. The target is stopped by the impact and the knife passes through the target. Determine the speed of the knife (in m/s) after passing through the target.

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Emiliano Montoya · Answer 1

We shall apply conservation of momentum here because it is a case of inelastic collision

u₁, u₂ initial velocity of knife and target. v₁, v₂ be their final velocity.

m₁ u₁ + m₂u₂ = m₁v₁ + m₂v₂

u₂ will be negative as it is coming from opposite direction.

36 x 22.5 - 300 x 2.45 = 22.5 x v₁ + 0

810 - 735 = 22.5 x v₁

v₁ = 3.33 m / s