Question

A knife thrower throws a knife toward a 300-g target that is sliding in her direction at a speed of 2.15 m/s on a horizontal frictionless surface. She throws a 22.5-g knife at the target with a speed of 39.0 m/s. The target is stopped by the impact and the knife passes through the target. Determine the speed of the knife after passing through the target.

Answer 1

Answer:

$v_{1f}$  = 10.3 m/s

Explanation:

We can solve this exercise using the conservation of the moment; the system is formed by the knife and the target, with an isolated system the moment is conserved during the collision

Knife mass m = 22.5 g and its velocity v₁₀ = 39 m / s, the mass of white is M = 300 gr and its velocity is v₂₀ = -2.15 m / s

Before the crash

     p₀ = m v₁₀ + M v₂₀

After the crash

    $p_{f}$ = m v₁ₐ + 0

    p₀ = $p_{f}$

   m v₁₀ + M v₂₀ = m $v_{1f}$

   $v_{1f}$  = (m v₁₀ + M v₂₀) / m

Let's calculate

  $v_{1f}$  = (0.0225 39.0 + 0.300 (-2.15)) / 0.0225

  $v_{1f}$  = 10.3 m / s